This invention relates to high speed black-and-white photothermographic materials that comprise very thin tabular grain silver halide emulsions. It is particularly directed to photothermographic materials useful for X-ray radiographic imaging. The invention also relates to methods of imaging using these materials. This invention is directed to the photothermographic imaging industry.
Silver-containing photothermographic imaging materials that are developed with heat and without liquid development have been known in the art for many years. Such materials are used in a recording process wherein an image is formed by imagewise exposure of the photothermographic material to specific electromagnetic radiation (for example, visible, ultraviolet, or infrared radiation) and developed by the use of thermal energy. These materials, also known as xe2x80x9cdry silverxe2x80x9d materials, generally comprise a support having coated thereon: (a) a photocatalyst (that is, a photosensitive compound such as silver halide) that upon such exposure provides a latent image in exposed grains that are capable of acting as a catalyst for the subsequent formation of a silver image in a development step, (b) a non-photosensitive source of reducible silver ions, (c) a reducing agent composition (usually including a developer) for the reducible silver ions, and (d) a hydrophilic or hydrophobic binder. The latent image is then developed by application of thermal energy.
In such materials, the photosensitive catalyst is generally a photographic type photosensitive silver halide that is considered to be in catalytic proximity to the non-photosensitive source of reducible silver ions. Catalytic proximity requires intimate physical association of these two components either prior to or during the thermal image development process so that when silver atoms (Ag0)n, also known as silver specks, clusters, nuclei or latent image, are generated by irradiation or light exposure of the photosensitive silver halide, those silver atoms are able to catalyze the reduction of the reducible silver ions within a catalytic sphere of influence around the silver atoms [D. H. Klosterboer, Imaging Processes and Materials, (Neblette""s Eighth Edition), J. Sturge, V. Walworth, and A. Shepp, Eds., Van Nostrand-Reinhold, New York, 1989, Chapter 9, pp. 279-291]. It has long been understood that silver atoms act as a catalyst for the reduction of silver ions, and that the photosensitive silver halide can be placed in catalytic proximity with the non-photosensitive source of reducible silver ions in a number of different ways (see, for example, Research Disclosure, June 1978, Item 17029). Other photosensitive materials, such as titanium dioxide, cadmium sulfide, and zinc oxide have also been reported to be useful in place of silver halide as the photocatalyst in photothermographic materials [see for example, Shepard, J. Appl. Photog. Eng. 1982, 8(5), 210-212, Shigeo et al., Nippon Kagaku Kaishi, 1994, 11, 992-997, and FR 2,254,047 (Robillard)].
The photosensitive silver halide may be made xe2x80x9cin-situ,xe2x80x9d for example by mixing an organic or inorganic halide-containing source with a source of reducible silver ions to achieve partial metathesis and thus causing the in-situ formation of silver halide (AgX) grains throughout the silver source [see, for example, U.S. Pat. No. 3,457,075 (Morgan et al.)]. In addition, photosensitive silver halides and sources of reducible silver ions can be coprecipitated [see Yu. E. Usanov et al., J. Imag. Sci. Tech. 1996, 40, 104]. Alternatively, a portion of the reducible silver ions can be completely converted to silver halide, and that portion can be added back to the source of reducible silver ions (see Yu. E. Usanov et al., International Conference on Imaging Science, Sep. 7-11, 1998, pp. 67-70).
The silver halide may also be xe2x80x9cpreformedxe2x80x9d and prepared by an xe2x80x9cex-situ xe2x80x9d process whereby the silver halide (AgX) grains are prepared and grown separately. With this technique, one has the possibility of controlling the grain size, grain size distribution, dopant levels, and composition much more precisely, so that one can impart more specific properties to both the silver halide grains and the photothermographic material. The preformed silver halide grains may be introduced prior to and be present during the formation of the source of reducible silver ions. Co-precipitation of the silver halide and the source of reducible silver ions provides a more intimate mixture of the two materials [see for example U.S. Pat. No. 3,839,049 (Simons)]. Alternatively, the preformed silver halide grains may be added to and physically mixed with the source of reducible silver ions.
The non-photosensitive source of reducible silver ions is a material that contains reducible silver ions. Typically, the preferred non-photosensitive source of reducible silver ions is a silver salt of a long chain aliphatic carboxylic acid having from 10 to 30 carbon atoms, or mixtures of such salts. Such acids are also known as xe2x80x9cfatty acidsxe2x80x9d or xe2x80x9cfatty carboxylic acids.xe2x80x9d Silver salts of other organic acids or other organic compounds, such as silver imidazoles, silver tetrazoles, silver benzotriazoles, silver benzotetrazoles, silver benzothiazoles and silver acetylides may also be used. U.S. Pat. No. 4,260,677 (Winslow et al.) discloses the use of complexes of various inorganic or organic silver salts.
In photothermographic materials, exposure of the photographic silver halide to light produces small clusters containing silver atoms (Ag0)n. The imagewise distribution of these clusters, known in the art as a latent image, is generally not visible by ordinary means. Thus, the photosensitive material must be further developed to produce a visible image. This is accomplished by the reduction of silver ions that are in catalytic proximity to silver halide grains bearing the silver-containing clusters of the latent image. This produces a black-and-white image. The non-photosensitive silver source in the exposed areas is catalytically reduced to form the visible black-and-white negative image while the silver halide and the non-photosensitive silver source in the unexposed areas are not reduced.
In photothermographic materials, the reducing agent for the reducible silver ions, often referred to as a xe2x80x9cdeveloper,xe2x80x9d may be any compound that, in the presence of the latent image, can reduce silver ion to metallic silver and is preferably of relatively low activity until it is heated to a temperature sufficient to cause the reaction. A wide variety of classes of compounds have been disclosed in the literature that function as developers for photothermographic materials. At elevated temperatures, the reducible silver ions are reduced by the reducing agent. In photothermographic materials, upon heating, this reaction occurs preferentially in the regions surrounding the latent image. This reaction produces a negative image of metallic silver having a color that ranges from yellow to deep black depending upon the presence of toning agents and other components in the imaging layer(s).
The imaging arts have long recognized that the field of photothermographyc is clearly distinct from that of photography. Photothermographic materials differ significantly from conventional silver halide photographic materials that require processing with aqueous processing solutions.
As noted above, in photothermographic imaging materials, a visible image is created by heat as a result of the reaction of a developer incorporated within the material. Heating at 50xc2x0 C. or more is essential for this dry development. In contrast, conventional photographic imaging materials require processing in aqueous processing baths at more moderate temperatures (from 30xc2x0 C. to 50xc2x0 C.) to provide a visible image.
In photothermographic materials, only a small amount of silver halide is used to capture light and a non-photosensitive source of reducible silver ions (for example a silver carboxylate) is used to generate the visible image using thermal development. Thus, the imaged photosensitive silver halide serves as a catalyst for the physical development process involving the non-photosensitive source of reducible silver ions and the incorporated reducing agent. In contrast, conventional wet-processed, black-and-white photographic materials use only one form of silver (that is, silver halide) that, upon chemical development, is itself at least partially converted into the silver image, or that upon physical development requires addition of an external silver source (or other reducible metal ions that form black images upon reduction to the corresponding metal). Thus, photothermographic materials require an amount of silver halide per unit area that is only a fraction of that used in conventional wet-processed photographic materials.
In photothermographic materials, all of the xe2x80x9cchemistryxe2x80x9d for imaging is incorporated within the material itself For example, such materials include a developer (that is, a reducing agent for the reducible silver ions) while conventional photographic materials usually do not. Even in so-called xe2x80x9cinstant photography,xe2x80x9d the developer chemistry is physically separated from the photo-sensitive silver halide until development is desired. The incorporation of the developer into photothermographic materials can lead to increased formation of various types of xe2x80x9cfogxe2x80x9d or other undesirable sensitometric side effects. Therefore, much effort has gone into the preparation and manufacture of photothermographic materials to minimize these problems during the preparation of the photothermographic emulsion as well as during coating, use, storage, and post-processing handling.
Moreover, in photothermographic materials, the unexposed silver halide generally remains intact after development and the material must be stabilized against further imaging and development. In contrast, silver halide is removed from conventional photographic materials after solution development to prevent further imaging (that is in the aqueous fixing step).
In photothermographic materials, the binder is capable of wide variation and a number of binders (both hydrophilic and hydrophobic) are useful. In contrast, conventional photographic materials are limited almost exclusively to hydrophilic colloidal binders such as gelatin.
Because photothermographic materials require dry thermal processing, they present distinctly different problems and require different materials in manufacture and use, compared to conventional, wet-processed silver halide photographic materials. Additives that have one effect in conventional silver halide photographic materials may behave quite differently when incorporated in photothermographic materials where the chemistry is significantly more complex. The incorporation of such additives as, for example, stabilizers, antifoggants, speed enhancers, supersensitizers, and spectral and chemical sensitizers in conventional photographic materials is not predictive of whether such additives will prove beneficial or detrimental in photothermographic materials. For example, it is not uncommon for a photographic antifoggant useful in conventional photographic materials to cause various types of fog when incorporated into photothermographic materials, or for supersensitizers that are effective in photographic materials to be inactive in photothermographic materials.
These and other distinctions between photothermographic and photographic materials are described in Imaging Processes and Materials (Neblette""s Eighth Edition), noted above, Unconventional Imaging Processes, E. Brinckman et al. (Eds.), The Focal Press, London and New York, 1978, pp. 74-75, in C. Zou et al., J. Imaging Sci. Technol. 1996, 40, pp. 94-103, and in M. R. V. Sahyun, J. Imaging Sci. Technol. 1998, 42, 23.
It has been reported in the literature that the use of silver halide tabular grain emulsions provides certain advantages over the use of cubic grain emulsions in photothermographic materials. However, the grain size requirement for tabular grain emulsions needed to achieve a reasonable aspect ratio has resulted in significant large grain volumes in comparison to cubic grain emulsions. These higher volumes generally introduce undesirably high Dmin and post-processing haze into the resulting images from the presence of undeveloped silver halide grains that cannot be removed.
Workers in the art have tried various approaches to solving this problem. One approach has been to reduce the size or equivalent circular diameter (ECD) of the tabular grain emulsions. The other approach has been to use silver chloride emulsions, thereby reducing light scattering in the resulting photothermographic imaging layers by virtue of the more favorable index of refraction for such grains.
U.S. Pat. No. 4,435,499 (Reeves) teaches the use of silver halide tabular grain emulsions in photothermographic materials containing silver behenate as the source of reducible silver ions. The tabular grains account for at least 70% of total grain projected area, have an average ECD in the range of from 0.30 to 0.45 xcexcm and an average aspect ratio of from 5 to 15.
U.S. Pat. No. 5,876,905 (Irving et al.) discloses a double-sided coated photothermographic imaging material comprising high chloride {1,0,0} tabular grain emulsions. Greater than 50% of total projected area of silver halide grains in these emulsions is provided by tabular grains having {1,0,0} major faces, containing greater than 70 mole % of silver chloride, exhibiting an average thickness of less than 0.3 xcexcm, and an average ECD of greater than 0.6 xcexcm. This material also includes silver behenate as the source of reducible silver ions and a hydrophobic binder.
EP-A-0 844 514 (Elst et al.) describes a photothermographic material containing silver halide tabular grains that contain more than 50 mole % of silver chloride and an average grain thickness of 0.2 xcexcm or less.
The use of small tabular grain emulsions, and particularly the use of silver chloride tabular grain emulsions, invariably reduces the photographic speed of the resulting imaging material. To obtain higher speed photothermographic materials, it is desirable to avoid high mole % silver chloride emulsions and preferred to use silver iodobromide tabular grain emulsions. Alternatively, one can use tabular grain emulsions with relatively large ECD to achieve higher photographic speed.
High-aspect ratio xe2x80x9cultrathinxe2x80x9d silver halide tabular grain emulsions have been used in recent years in conventional gelatin-based photographic materials to achieve certain photographic advantages such as improved image sharpness and silver efficiency. In these instances, xe2x80x9chigh-aspect ratio xe2x80x98ultrathinxe2x80x99 tabular grain emulsionsxe2x80x9d generally refer to those that have a mean tabular grain thickness of less than 0.08 xcexcm and an aspect ratio greater than 15:1. However, in such conventional xe2x80x9cwetxe2x80x9d processed photographic silver halide materials, the problem associated with post-processing haze after heat-development is not a concern since undeveloped silver halide is removed during xe2x80x9cwetxe2x80x9d processing using a conventional xe2x80x9cfixingxe2x80x9d step.
Photothermographic systems have not achieved wide use in X-radiography because of low speed, or high haze associated with the use of cubic or thick tabular grain silver halide emulsions. U.S. Pat. No. 4,480,024 (Lyons et al.) describes one attempt to overcome these problems by combining a specialized photothermographic coating and a rare-earth intensifying screen which are uniquely adapted to one another for the purpose of radiographic imaging. The photothermographic layer is dye-sensitized to the spectral emissions of the intensifying screen and the combination of screen and film is described as having an amplification factor greater or equal to at least 50.
EP-0 350 883 B1 (Pesce et al.) describes photothermographic materials having double-sided coatings that are sensitized to the wavelength of light emitted by an adjacent phosphor screen. Each adjacent phosphor screen emits at a different wavelength.
JP 2001109101 (Adachi) also describes a photothermographic material useful in X-radiography having photothermographic layers coated on both sides of the support. A coloring matter capable of being bleached by heat or light is included in the photosensitive layer or in at least one layer between the photothermographic layer and the support. The layer including the coloring matter is formed using  greater than 30% water as one of the coating solvents.
JP 2001-022027 (Adachi) also describes a double-sided photothermographic material useful in medical X-radiography having photothermographic layers coated on both sides of a polyethylene naphthalate support. The photosensitive silver halide is chemically sensitized by a chalcogen compound, and the reducing agent is included in a layer different from the layer including the photosensitive silver halide. The phosphor screen is laminated to the photothermographic coating.
There is a need for high-speed photothermographic materials that can be formulated in water and that provide images with low Dmin and low post-processing haze. Such photothermographic materials are particularly needed for radiographic imaging using X-radiation.
This invention provides a black-and-white photothermographic emulsion comprising:
a. a hydrophilic binder,
b. a non-photosensitive source of reducible silver ions, and
c. chemically sensitized photosensitive silver halide grains, at least 70% of the total photosensitive silver halide grain projected area being provided by tabular silver halide grains comprising at least 70 mole % bromide (based on total silver halide) with the remainder of the halide being iodide or chloride, the tabular grains having an average thickness of at least 0.02 xcexcm and up to and including 0.10 xcexcm, an equivalent circular diameter (ECD) of at least 0.5 xcexcm and up to and including 8 xcexcm, and an aspect ratio of at least 5:1.
This invention also provides a black-and-white photothermographic material comprising a support having thereon one or more hydrophilic layers each layer comprising a hydrophilic binder, and the photothermographic material further comprising on at least one side of the support, one or more thermally developable imaging layers comprising, in reactive association:
a. a non-photosensitive source of reducible silver ions,
b. a reducing agent composition for the reducible silver ions, and
c. chemically sensitized photosensitive silver halide grains, at least 70% of the total photosensitive silver halide grain projected area being provided by tabular silver halide grains comprising at least 70 mole % bromide (based on total silver halide) and the remainder of the halide being iodide or chloride, the tabular grains having an average thickness of at least 0.02 xcexcm and up to and including 0.10 xcexcm, an equivalent circular diameter of at least 0.5 xcexcm and up to and including 8 xcexcm, and an aspect ratio of at least 5:1.
This invention also provides preferred embodiments that are xe2x80x9cdouble-sidedxe2x80x9d photothermographic materials having one or more of the same or different thermally developable imaging layers as described above on both sides of the support.
Thus, in some preferred embodiments of this invention, a photothermographic material comprises a support having thereon two or more hydrophilic layers each layer comprising a hydrophilic binder, and the photothermographic material further comprises on both sides of the support, one or more of the same or different thermally developable imaging layers comprising, in reactive association:
a. a non-photosensitive source of reducible silver ions,
b. a reducing agent composition for the reducible silver ions, and
c. chemically sensitized photosensitive silver halide grains, at least 70% of the total photosensitive silver halide projected area being provided by tabular silver halide grains comprising at least 70 mole % bromide (based on total silver halide) and the remainder of the halide being iodide or chloride, the tabular grains having an average thickness of at least 0.02 xcexcm and up to and including 0.10 xcexcm, an equivalent circular diameter of at least 0.5 xcexcm and up to and including 8 xcexcm, and an aspect ratio of at least 5:1.
Particularly preferred embodiments of this invention include photothermographic materials comprising a support having thereon one or more hydrophilic layers each comprising a hydrophilic binder, and the photothermographic material further comprising on both sides of the support, one or more of the same thermally developable imaging layers comprising, in reactive association:
a. a non-photosensitive source of reducible silver ions,
b. a reducing agent composition for the reducible silver ions, and
c. chemically sensitized photosensitive silver halide grains, at least 85 mole % of the silver halide projected area being provided by tabular grains comprising at least 90 mole % bromide (based on total silver halide) and the remainder of the halide being iodide or chloride, the tabular grains having an average thickness of at least 0.03 and up to and including 0.08 xcexcm, an equivalent circular diameter of at least 0.75 and up to and including 6, and an aspect ratio of at least 10:1.
Further, this invention provides a method of forming a visible image comprising:
A) imagewise exposing the photothermographic material described above to electromagnetic radiation to form a latent image, and
B) simultaneously or sequentially, heating the exposed photothermographic material to develop the latent image into a visible image.
The photothermographic material may be exposed in step A) using any source of radiation to which it is sensitive, including ultraviolet light, visible light, near infrared radiation, infrared radiation, X-radiation, or any other radiation source readily apparent to one skilled in the art. Also suitable sources of radiation are light-emitting screen-cassette systems of X-ray radiation units.
In some embodiments, wherein the photothermographic material comprises a transparent support, the image-forming method further comprises:
C) positioning the exposed and heat-developed photothermographic material with the visible image thereon, between a source of imaging radiation and an imageable material that is sensitive to the imaging radiation, and
D) exposing the imageable material to the imaging radiation through the visible image in the exposed and heat-developed photothermographic material to provide an image in the imageable material.
In preferred embodiments, the method of forming a visible image comprises:
A) imagewise exposing the photothermographic materials (especially xe2x80x9cdouble-sidedxe2x80x9d photothermographic materials) described above to X-radiation to generate a latent image, and
B) simultaneously or sequentially, heating the exposed photothermographic material to develop the latent image into a visible image.
This imaging method is advantageously carried out using an imaging assembly of this invention comprising a black-and-white photothermographic material of this invention that is arranged in association with one or more phosphor intensifying screens.
The present invention provides a number of advantages with the use of very thin (xe2x80x9cultrathinxe2x80x9d) tabular grains as the predominant photosensitive silver halide. It was discovered that incorporation of high aspect ratio silver halide tabular grain emulsion with ultrathin thickness (that is, those with  less than 0.10 xcexcm thickness) and having specific equivalent circular diameter and aspect ratio into photothermographic emulsions provided images that exhibited reduced Dmin and reduced post-processing haze.
It was also discovered that such photothermographic imaging materials provide exceptionally high speed/silver efficiency ratio that can be attributed to the high surface area of such grains. While it is known that photographic speed is proportional to the grain size of silver halide crystals, for photothermographic materials having a given molar amount of silver halide grain coverage, larger grain size results in fewer centers for thermal development, or a smaller number of xe2x80x9cspheres of influence,xe2x80x9d thus reducing the silver efficiency.
However, for the xe2x80x9cultrathinxe2x80x9d tabular grain emulsions used in the present invention, the number of grains (per mole of silver) is much higher in comparison with a thicker tabular grain emulsion having a similar equivalent circular diameter, or a cubic grain emulsion with a similar edge length. This advantage results in excellent silver efficiency in photothermographic emulsions and materials and allowed such materials to be imaged using X-radiation.
These advantages are particularly noticeable in aqueous-based photothermographic imaging emulsions and materials that include silver benzotriazole or other heterocyclic silver salts as the non-photosensitive sources of reducible silver ions.
The photothermographic materials of this invention can be used in black-and-white photothermography and in electronically generated black-and-white hardcopy recording. They can be used in microfilm applications, in radiographic imaging (for example digital medical imaging), in X-ray radiography, and industrial radiography. Furthermore, the absorbance of these photothermographic materials between 350 and 450 nm is desirably low (less than 0.5), to permit their use in the graphic arts area (for example, imagesetting and phototypesetting), in the manufacture of printing plates, in contact printing, in duplicating (xe2x80x9cdupingxe2x80x9d), and in proofing.
The photothermographic materials of this invention are particularly useful for medical imaging of human or animal subjects in response to visible or X-radiation. Such applications include, but are not limited to, thoracic imaging, mammography, dental imaging, orthopedic imaging, general medical radiography, therapeutic radiography, veterinary radiography, and autoradiography. When used with X-radiation, the photothermographic materials of this invention may be used in combination with one or more phosphor intensifying screens. The materials of this invention are also useful for non-medical uses of visible or X-radiation (such as X-ray lithography and industrial radiography).
For some applications it may be useful that the photothermographic materials be xe2x80x9cdouble-sidedxe2x80x9d and have photothermographic coatings on both sides of the support.
The photothermographic materials of this invention can be sensitized to different regions of the spectrum, such as ultraviolet, visible, and infrered radiation. The photosensitive silver halide used in these materials has intrinsic sensitivity to blue light and to X-radiation. Increased sensitivity to a particular region of the spectrum is imparted through the use of various sensitizing dyes adsorbed to the silver halide grains.
In the photothermographic materials of this invention, the components needed for imaging can be in one or more thermally developable layers. The layer(s) that contain the photosensitive silver halide or non-photo-sensitive source of reducible silver ions, or both, are referred to herein as xe2x80x9cthermally developable layersxe2x80x9d or as xe2x80x9cphotothermographic emulsion layer(s).xe2x80x9d The photosensitive silver halide and the non-photosensitive source of reducible silver ions are in catalytic proximity (that is, in reactive association with each other) and preferably are in the same emulsion layer. xe2x80x9cCatalytic proximityxe2x80x9d or xe2x80x9creactive associationxe2x80x9d means that they should be in the same layer or in adjacent layers.
Where the materials contain imaging layers on one side of the support only, various non-imaging layers are usually disposed on the xe2x80x9cbacksidexe2x80x9d (non-emulsion side) of the materials, including antihalation layer(s), protective layers, antistatic layers, conductive layers, and transport enabling layers.
In such instances, various non-imaging layers can also be disposed on the xe2x80x9cfrontsidexe2x80x9d or emulsion side of the support, including protective topcoat layers, primer layers, interlayers, opacifying layers, antistatic layers, conductive layers, antihalation layers, acutance layers, auxiliary layers, and other layers readily apparent to one skilled in the art.
If the photothermographic materials comprise one or more thermally developable imaging layers on both sides of the support, each side can also include one or more protective topcoat layers, primer layers, interlayers, antistatic layers, conductive layers, acutance layers, auxiliary layers, crossover control layers, and other layers readily apparent to one skilled in the art.
When the photothermographic materials of this invention are thermally developed as described below in a substantially water-free condition after, or simultaneously with, imagewise exposure, a silver image (preferably a black-and-white silver image) is obtained.
As used herein:
In the descriptions of the photothermographic materials of the present invention, xe2x80x9caxe2x80x9d or xe2x80x9canxe2x80x9d component refers to xe2x80x9cat least onexe2x80x9d of that component (for example silver halides or toners).
Heating in a substantially water-free condition as used herein, means heating at a temperature of from about 50xc2x0 C. to about 250xc2x0 C. with little more than ambient water vapor present. The term xe2x80x9csubstantially water-free conditionxe2x80x9d means that the reaction system is approximately in equilibrium with water in the air and water for inducing or promoting the reaction is not particularly or positively supplied from the exterior to the material. Such a condition is described in T. H. James, The Theory of the Photographic Process, Fourth Edition, Eastrnan Kodak Company, Rochester, N.Y., 1977, p. 374.
xe2x80x9cPhotothermographic material(s)xe2x80x9d means a construction comprising at least one photothermographic emulsion layer or a photothermographic set of layers (wherein the silver halide and the source of reducible silver ions are in one layer and the other essential components or desirable additives are distributed, as desired, in an adjacent coating layer) and any supports, topcoat layers, image-receiving layers, antistatic layers, conductive layers, blocking layers, antihalation layers, subbing or priming layers. These materials also include multilayer constructions in which one or more imaging components are in different layers, but are in xe2x80x9creactive associationxe2x80x9d so that they readily come into contact with each other during imaging and/or development. For example, one layer can include the non-photosensitive source of reducible silver ions and another layer can include the reducing agent composition, but the two reactive components are in reactive association with each other.
xe2x80x9cPhotocatalystxe2x80x9d means a photosensitive compound such as silver halide that, upon exposure to radiation, provides a compound that is capable of acting as a catalyst for the subsequent development of the image-forming material.
xe2x80x9cCatalytic proximityxe2x80x9d or xe2x80x9creactive associationxe2x80x9d means that the materials are in the same layer or in adjacent layers so that they readily come into contact with each other during thermal imaging and development.
xe2x80x9cEmulsion layer,xe2x80x9d xe2x80x9cimaging layer,xe2x80x9d xe2x80x9cthermally developable imaging layer,xe2x80x9d or xe2x80x9cphotothermographic emulsion layer,xe2x80x9d means a layer of a photothermographic material that contains the photosensitive silver halide and/or non-photosensitive source of reducible silver ions. It can also mean a layer of the photothermographic material that contains, in addition to the photosensitive silver halide and/or non-photosensitive source of reducible ions, additional essential components and/or desirable additives. These layers are usually on what is known as the xe2x80x9cfrontsidexe2x80x9d of the support, but in some embodiments, they are present on both sides of the support. Such embodiments are known as xe2x80x9cdouble-sidedxe2x80x9d photothermographic materials. In such double-sided materials the layers can be of the same or different chemical composition, thickness, or sensitometric properties.
xe2x80x9cUltraviolet region of the spectrumxe2x80x9d refers to that region of the spectrum less than or equal to 410 nm, and preferably from about 100 nm to about 410 nm, although parts of these ranges may be visible to the naked human eye. More preferably, the ultraviolet region of the spectrum is the region of from about 190 to about 405 nm.
xe2x80x9cVisible region of the spectrumxe2x80x9d refers to that region of the spectrum of from about 400 nm to about 700 nm.
xe2x80x9cShort wavelength visible region of the spectrumxe2x80x9d refers to that region of the spectrum of from about 400 nm to about 450 nm.
xe2x80x9cRed region of the spectrumxe2x80x9d refers to that region of the spectrum of from about 600 nm to about 700 nm.
xe2x80x9cInfrared region of the spectrumxe2x80x9d refers to that region of the spectrum of from about 700 nm to about 1400 nm.
xe2x80x9cNon-photosensitivexe2x80x9d means intentionally neither light nor radiation sensitive.
The sensitometric terms xe2x80x9cspeed,xe2x80x9d xe2x80x9cphotospeedxe2x80x9d or xe2x80x9cphotographic speedxe2x80x9d (also known as xe2x80x9csensitivityxe2x80x9d), xe2x80x9cabsorbance,xe2x80x9d xe2x80x9ccontrast,xe2x80x9d Dmin, and Dmax have conventional definitions known in the imaging arts. Particularly, Dmin is considered herein as image density achieved when the photothermographic material is thermally developed without prior exposure to radiation.
xe2x80x9cTransparentxe2x80x9d means capable of transmitting visible light or imaging radiation without appreciable scattering or absorption.
The term xe2x80x9cequivalent circular diameterxe2x80x9d (ECD) is used to define the diameter (xcexcm) of a circle having the same projected area as a silver halide grain.
The term xe2x80x9caspect ratioxe2x80x9d is used to define the ratio of grain ECD to grain thickness.
The term xe2x80x9ctabular grainxe2x80x9d is used to define a silver halide grain having two parallel crystal faces that are clearly larger than any remaining crystal faces and having an aspect ratio of at least 2. The term xe2x80x9ctabular grain emulsionxe2x80x9d herein refers to an imaging emulsion containing silver halide grains in which the tabular grains account for more than 70% of the total photosensitive silver halide grain projected area.
The terms xe2x80x9cdouble-sidedxe2x80x9d and xe2x80x9cdouble-faced coatingxe2x80x9d are used to define photothermographic materials having one or more of the same or different thermally developable emulsion layers disposed on both sides (front and back) of the support.
In the compounds described herein, no particular double bond geometry (for example, cis or trans) is intended by the structures drawn. Similarly, alternating single and double bonds and localized charges are drawn as a formalism. In reality, both electron and charge delocalization exists throughout the conjugated chain.
As is well understood in this art, for all organic compounds herein described, substitution is not only tolerated, but is often advisable and various substituents are anticipated on the compounds used in the present invention unless otherwise stated. Thus, when a compound is referred to as xe2x80x9chaving the structurexe2x80x9d of a given formula, any substitution that does not alter the bond structure of the formula or the shown atoms within that structure is included within the formula, unless such substitution is specifically excluded by language (such as xe2x80x9cfree of carboxy-substituted alkylxe2x80x9d). For example, where a benzene ring structure is shown (including fused ring structures), substituent groups may be placed on the benzene ring structure, but the atoms making up the benzene ring structure may not be replaced.
As a means of simplifying the discussion and recitation of certain substituent groups, the term xe2x80x9cgroupxe2x80x9d refers to chemical species that may be substituted as well as those that are not so substituted. Thus, the term xe2x80x9cgroup,xe2x80x9d such as xe2x80x9calkyl groupxe2x80x9d is intended to include not only pure hydrocarbon alkyl chains, such as methyl, ethyl, n-propyl, t-butyl, cyclohexyl, iso-propyl, and octadecyl, but also alkyl chains bearing substituents known in the art, such as hydroxyl, alkoxy, phenyl, halogen atoms (F, Cl, Br, and I), cyano, nitro, amino, and carboxy. For example, alkyl group includes ether and thioether groups (for example CH3xe2x80x94CH2xe2x80x94CH2xe2x80x94Oxe2x80x94CH2xe2x80x94 and CH3xe2x80x94CH2xe2x80x94CH2xe2x80x94Sxe2x80x94CH2xe2x80x94), haloalkyl, nitroalkyl, alkylcarboxy, carboxyalkyl, carboxamido, hydroxyalkyl, sulfoalkyl, and other groups readily apparent to one skilled in the art. Substituents that adversely react with other active ingredients, such as very strongly electrophilic or oxidizing substituents, would, of course, be excluded by the ordinarily skilled artisan as not being inert or harmless.
Research Disclosure is a publication of Kenneth Mason Publications Ltd., Dudley House, 12 North Street, Emsworth, Hampshire PO10 7DQ England (also available from Emsworth Design Inc., 147 West 24th Street, New York, N.Y. 10011).
Other aspects, advantages, and benefits of the present invention are apparent from the detailed description, examples, and claims provided in this application.
As noted above, the photothermographic materials of the present invention include one or more silver halides that comprise at least 70 mole % (preferably at least 85 mole % and more preferably at least 90 mole %) bromide (based on total silver halide). The remainder of the halide is either iodide or chloride, or both. Preferably, the additional halide is iodide.
Such useful silver halides include pure silver bromide and mixed silver halides such as silver bromoiodide, silver bromoiodochloride, and silver bromochloride as long as the bromide comprises at least 70 mole % of the total halide content. Mixtures of these silver halides can also be used in any suitable proportion as long as bromide comprises at least 70 mole % of the total halides in the mixtures. Silver bromide and silver bromoiodide are more preferred, with the latter silver halide having up to 15 mole % iodide (based on total silver halide) and more preferably, up to 10 mole % iodide.
Moreover, at least 70% (preferably from about 85% to 100%) of the total photosensitive silver halide grain projected area in each emulsion used in the invention are tabular silver halide grains having an aspect ratio of at least 5. The remainder of the silver halide grains can have any suitable crystalline habit including, but not limited to, cubic, octahedral, tetrahedral, orthorhombic, rhombic, dodecahedral, other polyhedral, laminar, twinned, or platelet morphologies and may have epitaxial growth of crystals thereon. If desired, a mixture of these crystals can be employed. Most preferably, substantially all of the silver halide grains have tabular morphology.
The tabular silver halide grains used in the practice of this invention are advantageous because they are considered xe2x80x9cultrathinxe2x80x9d and have an average thickness of at least 0.02 xcexcm and up to and including 0.10 xcexcm. Preferably, they have an average thickness of at least 0.03 xcexcm and more preferably of at least 0.04 xcexcm, and up to and including 0.08 xcexcm and more preferably up to and including 0.07 xcexcm.
In addition, these tabular grains have an ECD of at least 0.5 xcexcm, preferably at least 0.75 xcexcm, and more preferably at least 1.0 xcexcm. The ECD can be up to and including 8 xcexcm, preferably up to and including 6 xcexcm, and more preferably up to and including 4 xcexcm.
The aspect ratio of the useful tabular grains is at least 5:1, preferably at least 10:1, and more preferably at least 15:1. For practical purposes, the tabular grain aspect ratio is generally up to 100:1. An aspect ratio of between about 30:1 and about 70:1 is particularly useful.
Grain size may be determined by any of the methods commonly employed in the art for particle size measurement. Representative methods are described, for example, in xe2x80x9cParticle Size Analysis,xe2x80x9d ASTM Symposium on Light Microscopy, R. P. Loveland, 1955, pp. 94-122, and in C. E. K. Mees and T. H. James, The Theory of the Photographic Process, Third Edition, Macmillan, New York, 1966, Chapter 2. Particle size measurements may be expressed in terms of the projected areas of grains or approximations of their diameters. These will provide reasonably accurate results if the grains of interest are substantially uniform in shape. In the Examples below, the grain sizes referred to were determined using well-known electron microscopy techniques such as Transmission Electron Microscopy (TEM) or Scanning Electron Microscopy (SEM).
As noted above, the high aspect ratio tabular silver halide grains useful in the present invention generally have a uniform ratio of halide throughout. However, they may have a graded halide content, with a continuously varying ratio of, for example, silver bromide and silver iodide or they may be of the core-shell type, having a discrete core of one halide ratio, and one or more discrete shells of another halide ratio. For example, the central regions of the tabular grains may contain at least 1 mol % more iodide than outer or annular regions of the grains. Core-shell silver halide grains useful in photothermographic materials and methods of preparing these materials are described for example in U.S. Pat. No. 5,382,504 (Shor et al.), incorporated herein by reference. Iridium and/or copper doped core-shell and non-core-shell grains are described in U.S. Pat. No. 5,434,043 (Zou et al.) and U.S. Pat. No. 5,939,249 (Zou), both incorporated herein by reference.
The tabular silver halide grains can also be doped using one or more of the conventional metal dopants known for this purpose including those described in Research Disclosure September 1996, Item 38957, and U.S. Pat. No. 5,503,970 (Olm et al.), incorporated herein by reference. Preferred dopants include iridium (3+ or 4+) and ruthenium (2+ or 3+) salts.
The tabular grain photosensitive silver halide can be added to (or formed within) the emulsion layer(s) in any fashion as long as it is placed in catalytic proximity to the non-photosensitive source of reducible silver ions.
It is preferred that the tabular silver halide grains be preformed and prepared by an ex-situ process. The silver halide grains prepared ex-situ may then be added to and physically mixed with the non-photosensitive source of reducible silver ions.
The source of reducible silver ions may also be formed in the presence of ex-situ-prepared tabular silver halide grains. In this process, the source of reducible silver ions, is formed in the presence of these preformed silver halide grains. Co-precipitation of the reducible source of silver ions in the presence of silver halide provides a more intimate mixture of the two materials [see, for example U.S. Pat. No. 3,839,049 (Simons)]. Materials of this type are often referred to as xe2x80x9cpreformed soaps.xe2x80x9d
Mixing of the tabular silver halide grains prepared ex-situ with the non-photosensitive silver source can also be carried out during the coating step using, for example, in-line mixing techniques.
Preformed tabular grain silver halide emulsions used in the material of this invention can be prepared by aqueous or organic processes and can be unwashed or washed to remove soluble salts. In the latter case, the soluble salts can be removed by ultrafiltration, by chill setting and leaching, or by washing the coagulum [for example, by the procedures described in U.S. Pat. No. 2,618,556 (Hewitson et al.), U.S. Pat. No. 2,614,928 (Yutzy et al.), U.S. Pat. No. 2,565,418 (Yackel), U.S. Pat. No. 3,241,969 (Hart et al.), and U.S. Pat. No. 2,489,341 (Waller et al.)].
Additional methods of preparing these silver halide and organic silver salts and manners of blending them are described in Research Disclosure, June 1978, Item 17029, U.S. Pat. No. 3,700,458 (Lindholm) and U.S. Pat. No. 4,076,539 (Ikenoue et al.), and JP Applications 13224/74, 42529/76, and 17216/75.
In some instances, it may be helpful to prepare the photosensitive tabular silver halide grains in the presence of a hydroxytetrazindene (such as 4-hydroxy-6-methyl-1,3,3a,7-tetrazaindene) or a N-heterocyclic compound comprising at least one mercapto group (such as 1-phenyl-5-mercaptotetrazole). Details of this procedure are provided in copending and commonly assigned U.S. Ser. No. 09/833,533 (filed Apr. 12, 2001 by Shor, Zou, Ulrich, and Simpson), that is incorporated herein by reference.
A useful method of preparing the xe2x80x9cultrathinxe2x80x9d tabular silver halide grains useful in the practice of this invention are exemplified below just prior to the Examples.
In addition to the preformed tabular silver halide grains, it is also effective to use an in-situ process in which a halide-containing compound is added to an organic silver salt to partially convert some of the silver of the organic silver salt to silver halide. The halogen-containing compound can be inorganic (such as zinc bromide or lithium bromide) or organic (such as N-bromosuccinimide)
The one or more light-sensitive tabular silver halides used in the photothermographic materials of the present invention are preferably present in an amount of from about 0.005 to about 0.5 mole, more preferably from about 0.05 to about 0.30 mole, and most preferably from about 0.01 to about 0.25 mole, per mole of non-photosensitive source of reducible silver ions.
The photosensitive silver halide used in the present invention may be employed without modification. However, it may be chemically sensitized with one or more chemical sensitizing agents such as compounds containing sulfur, selenium, or tellurium, a compound containing gold, platinum, palladium, iron, ruthenium, rhodium, or iridium, a reducing agent such as a tin halide. The details of these procedures are described in T. H. James, The Theory of the Photographic Process, Fourth Edition, Eastman Kodak Company, Rochester, N.Y., 1977, Chapter 5, pages 149 to 169, U.S. Pat. No. 1,623,499 (Sheppard et al.), U.S. Pat. No. 2,399,083 (Waller et al.), U.S. Pat. No. 3,297,447 (McVeigh), U.S. Pat. No. 3,297,446 (Dunn), U.S. Pat. No. 5,049,485 (Deaton), U.S. Pat. No. 5,252,455 (Deaton), U.S. Pat. No. 5,391,727 (Deaton), U.S. Pat. No. 5,912,111 (Lok et al.), U.S. Pat. No. 5,759,761 (Lushington et al.), U.S. Pat. No. 5,945,270 (Lok et al.), U.S. Pat. No. 6,159,676 (Lin et al), and U.S. Pat. No. 6,296,998 (Eikenberry et al).
In addition, tabular silver halide grains comprising sensitizing dye(s), silver salt epitaxial deposits, and addenda that include a mercaptotetrazole and a tetraazindene may be chemically sensitized. Such emulsions are described in U.S. Pat. No. 5,691,127 (Daubendiek et al.), incorporated herein by reference.
Sulfur sensitization is performed by adding a sulfur sensitizer and stirring the emulsion at a temperature as high as 40xc2x0 C. or above for a predetermined time. In addition to the sulfur compound contained in gelatin, various sulfur compounds can be used. Some examples of sulfur sensitizers include thiosulfates (for example, hypo), thioureas (for example, diphenylthiourea, triethylthiourea, N-ethyl-Nxe2x80x2-(4-methyl-2-thiazolyl)thiourea and certain tetrasubstituted thioureas known as xe2x80x9crapid sulfiding agentsxe2x80x9d), thioamides (for example, thioacetamide), rhodanines (for example, diethylrhodanine and 5-benzylidene-N-ethylrhodanine), phosphine sulfides (for example, trimethylphosphine sulfide), thiohydantoins, 4-oxo-oxazolidine-2-thiones, dipolysulfides (fox example, dimorpholine disulfide, cystine and hexathiocane-thione), mercapto compounds (for example, cystein), polythionates, and elemental sulfur.
Rapid sulfiding agents are also useful in the present invention. Particularly useful are the tetrasubstituted middle chalcogen thiourea compounds represented below by Structure RS-1: 
wherein each Ra, Rb, Rc, and Rd group independently represents an alkylene, cycloalkylene, carbocyclic arylene, heterocyclic arylene, alkarylene or aralkylene group, or taken together with the nitrogen atom to which they are attached, Ra and Rb or Rc, and Rd can complete a 5- to 7-membered heterocyclic ring, and each of the Ba, Bb, Bc, and Bd groups independently is hydrogen or represents a carboxylic, sulfinic, sulfonic, hydroxamic, mercapto, sulfonamido or primary or secondary amino nucleophilic group, with the proviso that at least one of the RaBa, through RdBd groups contains the nucleophilic group bonded to a urea nitrogen atom through a 1- or 2-membered chain. Tetrasubstituted middle chalcogen ureas of such formula are disclosed in U.S. Pat. No. 4,810,626 (Burgmaier et al.), the disclosure of which is here incorporated by reference.
A preferred group of rapid sulfiding agents has the general structure RS-1 is that wherein each of the Ra, Rb, Rc, and Rd groups independently represents an alkylene group having 1 to 6 carbon atoms, and each of the Ba, Bb, Bc, and Bd groups independently is hydrogen or represents a carboxylic, sulfinic, sulfonic, hydroxamic group, with the proviso that at least one of the RaBa through R4B4 groups contains the nucleophilic group bonded to a urea nitrogen atom through a 1- or 2-membered chain. Especially preferred rapid sulfiding agents are represented by Structures RS-1a and RS-1b: 
These compounds have been shown to be very effective sensitizers under mild digestion conditions and to produce higher speeds than many other thiourea compounds that lack the specified nucleophilic substituents.
The amount of the sulfur sensitizer to be added varies depending upon various conditions such as pH, temperature and grain size of silver halide at the time of chemical ripening, it is preferably from 10xe2x88x927 to 10xe2x88x922 mole per mole of silver halide, and more preferably from 10xe2x88x925 to 10xe2x88x923 mole.
Selenium sensitization is performed by adding a selenium compound and stirring the emulsion at a temperature at least 40xc2x0 C. for a predetermined time. Examples of the selenium sensitizers include colloidal selenium, selenoureas (for example, N,N-dimethylselenourea, trifluoromethyl-carbonyl-trimethylselenourea and acetyl-trimethylselenourea), selenoamides (for example, selenoacetamide and N,N-diethylphenylselenoamide), phosphine selenides (for example, triphenylphosphine selenide and pentafluorophenyl-triphenylphosphine selenide, and methylene-bis[diphenyl-phosphine selenide), selenophoshpates (for example, tri-p-tolyl-selenophosphate and tri-n-butyl seleno-phosphate), selenoketones (for example, selenobenzophenone), isoselenocyanates, selenocarboxylic acids, selenoesters and diacyl selenides. Other selenium compounds such as selenious acid, potassium selenocyanate, selenazoles, and selenides can also be used as selenium sensitizers. Some specific examples of useful selenium compounds can be found in U.S. Pat. No. 5,158,892 (Sasaki et al.), U.S. Pat. No. 5,238,807 (Sasaki et al.), and U.S. Pat. No. 5,942,384 (Arai et al.). Still other useful selenium sensitizers are those described in co-pending and commonly assigned U.S. Ser. No. 10/082,516 (filed Feb. 25, 2002 by Lynch, Opatz, Gysling, and Simpson), incorporated herein by reference.
Tellurium sensitizers for use in the present invention are compounds capable of producing silver telluride, which is presumed to serve as a sensitization nucleus on the surface or inside of silver halide grain. Examples of the tellurium sensitizers include telluroureas (for example, tetramethyltellurourea, N,N-dimethylethylene-tellurourea and N,Nxe2x80x2-diphenylethylenetellurourea), phosphine tellurides (for example, butyl-diisopropylphosphine telluride, tributylphosphine telluride, tributoxyphosphine telluride and ethoxy-diphenylphosphine telluride), diacyl ditellurides and diacyl tellurides [for example, bis(diphenylcarbamoyl ditelluride, bis(N-phenyl-N-methylcarbamoyl) ditelluride, bis(N-phenyl-N-methylcarbamoyl) telluride and bis(ethoxycarbonyl telluride)], isotellurocyanates, telluroamides, tellurohydrazides, telluroesters (such as butyl hexyl telluroester), telluroketones (such as telluroacetophenone), colloidal tellurium, (di)tellurides and other tellurium compounds (for example, potassium telluride and sodium telluropentathionate). Tellurium compounds for use as chemical sensitizers can be selected from those described in J. Chem. Soc,. Chem. Commun. 1980, 635, ibid., 1979, 1102, ibid., 1979, 645, J. Chem. Soc. Perkin. Trans, 1980, 1, 2191, The Chemistry of Organic Selenium and Tellurium Compounds, S. Patai and Z. Rappoport, Eds., Vol. 1 (1986), and Vol. 2 (1987) and U.S. Pat. No. 5,677,120 (Lushington et al.). Preferred tellurium-containing chemical sensitizers are those described in copending and commonly assigned U.S. Ser. No. 09/975,909 (filed Oct. 11, 2001 by Lynch, Opatz, Shor, Simpson, Willett, and Gysling) and in co-pending and commonly assigned U.S. Ser. No. 09/923,039 (filed Aug. 6, 2001 by Gysling, Dickinson, Lelental, and Boettcher), both incorporated herein by reference.
Specific examples thereof include the compounds described in U.S. Pat. No. 1,623,499 (Sheppard et al.), U.S. Pat. No. 3,320,069 (Illingsworth), U.S. Pat. No. 3,772,031 (Berry et al.), U.S. Pat. No. 5,215,880 (Kojima et al.), U.S. Pat. No. 5,273,874 (Kojima et al.), U.S. Pat. No. 5,342,750 (Sasaki et al.), British Patent 235,211 (Sheppard), British Patent 1,121,496 (Halwig), British Patent 1,295,462 (Hilson et al.) and British Patent 1,396,696 (Simons), and JP-04-271341 A (Morio et al.).
The amount of the selenium or tellurium sensitizer used in the present invention varies depending on silver halide grains used or chemical ripening conditions. However, it is generally from 10xe2x88x928 to 10xe2x88x922 mole per mole of silver halide, preferably on the order of from 10xe2x88x927 to 10xe2x88x923 mole. The conditions for chemical sensitization in the present invention are not particularly restricted. However, in general, pH is from 5 to 8, pAg is from 6 to 11, preferably from 7 to 10, and temperature is from 40 to 95xc2x0 C., preferably from 45 to 85xc2x0 C.
Noble metal sensitizers for use in the present invention include gold, platinum, palladium and iridium. Gold sensitization is particularly preferred.
The gold sensitizer used for the gold sensitization of the silver halide emulsion used in the present invention may have an oxidation number of 1 or 3, and may be a gold compound commonly used as a gold sensitizer. Examples thereof include chloroauric acid, potassium chloroaurate, auric trichloride, potassium dithiocyanatoaurate, [AuS2P(i-C4H9)2]2, bis-(1,4,5-trimethyl-1,2,4-triazolium-3-thiolate) gold (I) tetrafluoroborate, and pyridyltrichloro gold. U.S. Pat. No. 5,858,637 (Eshelman et al.) describes various Au (I) compounds that can be used as chemical sensitizers. Other useful gold compounds can be found in U.S. Pat. No. 5,759,761 (Lushington et al.).
Useful combinations of gold (I) complexes and rapid sulfiding agents are described in U.S. Pat. No. 6,322,961 (Lam et al.). Combinations of gold (III) compounds and either sulfur or tellurium compounds are useful as chemical sensitizers and are described in co-pending and commonly assigned U.S. Ser. No. 09/768,094 (filed Jan. 23, 2001 by Simpson, Shor, and Whitcomb), incorporated herein by reference.
Production or physical ripening processes for the silver halide grains used in emulsions of the present invention may be performed under the presence of cadmium salts, sulfites, lead salts, or thallium salts.
Reduction sensitization may also be used. Specific examples of compounds useful in reduction sensitization include, but are not limited to, stannous chloride, hydrazine ethanolamine, and thioureaoxide. Reduction sensitization may be performed by ripening the grains while keeping the emulsion at pH 7 or above, or at pAg 8.3 or less. Also, reduction sensitization may be performed by introducing a single addition portion of silver ion during the formation of the grains.
In general, it may also be desirable to add spectral sensitizing dyes to enhance silver halide sensitivity to ultraviolet, visible, and/or infrared radiation. Thus, the photosensitive silver halides may be spectrally sensitized with various dyes that are known to spectrally sensitize silver halide. Non-limiting examples of sensitizing dyes that can be employed include cyanine dyes, merocyanine dyes, complex cyanine dyes, complex merocyanine dyes, holopolar cyanine dyes, hemicyanine dyes, styryl dyes, and hemioxanol dyes. Cyanine dyes, merocyanine dyes and complex merocyanine dyes are particularly useful.
Suitable sensitizing dyes such as those described in U.S. Pat. No. 3,719,495 (Lea), U.S. Pat. No. 4,396,712 (Kinoshita et al.), U.S. Pat. No. 4,690,883 (Kubodera et al.), U.S. Pat. No. 4,840,882 (Iwagaki et al.), U.S. Pat. No. 5,064,753 (Kohno et al.), U.S. Pat. No. 5,281,515 (Delprato et al.), U.S. Pat. No. 5,393,654 (Burrows et al.), U.S. Pat. No. 5,441,866 (Miller et al.), U.S. Pat. No. 5,508,162 (Dankosh), U.S. Pat. No. 5,510,236 (Dankosh), U.S. Pat. No. 5,541,054 (Miller et al.), JP 2000-063690 (Tanaka et al.), JP 2000-112054 (Fukusaka et al.), JP 2000-273329 (Tanaka et al.), JP 2001-005145 (Arai), JP 2001064527 (Oshiyama et al.), and JP 2001-154305 (Kita et al.), can be used in the practice of the invention. All of the publications noted above are incorporated herein by reference.
A summary of generally useful spectral sensitizing dyes is contained in Research Disclosure, Item 308119, Section IV, December, 1989. Additional teaching relating to specific combinations of spectral sensitizing dyes also include U.S. Pat. No. 4,581,329 (Sugimoto et al.), U.S. Pat. No. 4,582,786 (Ikeda et al.), U.S. Pat., U.S. Pat. No. 4,609,621 (Sugimoto et al.), U.S. Pat. No. 4,675,279 (Shuto et al.), U.S. Pat. No. 4,678,741 (Yamada et al.), U.S. Pat. No. 4,720,451 (Shuto et al.), U.S. Pat. No. 4,818,675 (Miyasaka et al.), U.S. Pat. No. 4,945,036 (Arai et al.), and U.S. Pat. No. 4,952,491 (Nishikawa et al.). Additional classes of dyes useful for spectral sensitization, including sensitization at other wavelengths are described in Research Disclosure, 1994, Item 36544, section V. All of the above references and patents above are incorporated herein by reference.
Also useful are spectral sensitizing dyes that decolorize by the action of light or heat. Such dyes are described in U.S. Pat. No. 4,524,128 (Edwards et al.), JP 2001109101 (Adachi), JP 2001-154305 (Kita et al.), and JP 2001-183770 (Hanyu et al.).
Spectral sensitizing dyes are chosen for optimum photosensitivity, stability, and synthetic ease. They may be added before, after, or during the chemical finishing of the photothermographic emulsion. One useful spectral sensitizing dye for the photothermographic materials of this invention is anhydro-5-chloro-3,3xe2x80x2-di-(3-sulfopropyl)naphtho[1,2-d]thiazolothiacyanine hydroxide, triethylammonium salt.
Spectral sensitizing dyes may be used singly or in combination. When used singly or in combination, the dyes are selected for the purpose of adjusting the wavelength distribution of the spectral sensitivity, and for the purpose of supersensitization. When using a combination of dyes having a supersensitizing effect, it is possible to attain much higher sensitivity than the sum of sensitivities that can be achieved by using each dye alone. It is also possible to attain such supersensitizing action by the use of a dye having no spectral sensitizing action by itself, or a compound that does not substantially absorb visible light. Diaminostilbene compounds are often used as supersensitizers.
An appropriate amount of spectral sensitizing dye added is generally about 10xe2x88x9210 to 10xe2x88x921 mole, and preferably, about 10xe2x88x927 to 10xe2x88x922 mole per mole of silver halide.
The non-photosensitive source of reducible silver ions used in photothermographic materials of this invention can be any organic compound that contains reducible silver (1+) ions. Preferably, it is a silver salt or coordination complex that is comparatively stable to light and forms a silver image when heated to 50xc2x0 C. or higher in the presence of an exposed silver halide and a reducing agent composition.
Silver salts of nitrogen-containing heterocyclic compounds are preferred, and one or more silver salts of compounds containing an imino group are particularly preferred. Representative compounds of this type include, but are not limited to, silver salts of benzotriazole and substituted derivatives thereof (for example, silver methylbenzotriazole and silver 5-chlorobenzotriazole), silver salts of 1,2,4-triazoles or 1-H-tetrazoles such as phenylmercaptotetrazole as described in U.S. Pat. No. 4,220,709 (deMauriac), and silver salts of imidazoles and imidazole derivatives as described in U.S. Pat. No. 4,260,677 (Winslow et al.). Particularly useful silver salts of this type are the silver salts of benzotriazole, substituted derivatives thereof, or mixtures of two or more of these salts. A silver salt of benzotriazole is most preferred in the photothermographic emulsions and materials of this invention.
Silver salts of compounds containing mercapto or thione groups and derivatives thereof can also be used. Preferred compounds of this type include a heterocyclic nucleus containing 5 or 6 atoms in the ring, at least one of which is a nitrogen atom, and other atoms being carbon, oxygen, or sulfur atoms. Such heterocyclic nuclei include, but are not limited to, triazoles, oxazoles, thiazoles, thiazolines, imidazoles, diazoles, pyridines, and triazines. Representative examples of these silver salts include, but are not limited to, a silver salt of 3-mercapto-4-phenyl-1,2,4-triazole, a silver salt of 2-mercapto-benzimidazole, a silver salt of 2-mercapto-5-aminothiadiazole, a silver salt of 2-(2-ethylglycolamido)benzothiazole, a silver salt of 5-carboxylic-1-methyl-2-phenyl-4-thiopyridine, a silver salt of mercaptotriazine, a silver salt of 2-mercaptobenzoxazole, silver salts as described in U.S. Pat. No. 4,123,274 (Knight et al.) (for example, a silver salt of a 1,2,4-mercaptothiazole derivative, such as a silver salt of 3-amino-5-benzylthio-1,2,4-thiazole), and a silver salt of thione compounds [such as a silver salt of 3-(2-carboxyethyl)-4-methyl-4-thiazoline-2-thione as described in U.S. Pat. No. 3,785,830 (Sullivan et al.)]. Examples of other useful silver salts of mercapto or thione substituted compounds that do not contain a heterocyclic nucleus include but are not limited to, a silver salt of thioglycolic acids such as a silver salt of an S-alkylthioglycolic acid (wherein the alkyl group has from 12 to 22 carbon atoms), a silver salt of a dithiocarboxylic acid such as a silver salt of a dithioacetic acid, and a silver salt of a thioamide.
Suitable organic silver salts include silver salts of organic compounds having a carboxylic acid group can also be used. Examples thereof include a silver salt of an aliphatic carboxylic acid (for example, having 10 to 30 carbon atoms in the fatty acid) or a silver salt of an aromatic carboxylic acid. Preferred examples of the silver salts of aliphatic carboxylic acids include silver behenate, silver arachidate, silver stearate, silver oleate, silver laurate, silver caprate, silver myristate, silver palmitate, silver maleate, silver fumarate, silver tartarate, silver furoate, silver linoleate, silver butyrate, silver camphorate, and mixtures thereof. When silver carboxylates are used, silver behenate is used alone or in mixtures with other silver salts.
In some embodiments of this invention, a mixture of a silver carboxylate and a silver salt of a compound having an imino group can be used.
Representative examples of the silver salts of aromatic carboxylic acid and other carboxylic acid group-containing compounds include, but are not limited to, silver benzoate, and silver substituted-benzoates, (such as silver 3,5-dihydroxy-benzoate, silver o-methylbenzoate, silver m-methylbenzoate, silver p-methylbenzoate, silver 2,4-dichlorobenzoate, silver acetamidobenzoate, silver p-phenylbenzoate, silver tannate, silver phthalate, silver terephthalate, silver salicylate, silver phenylacetate, and silver pyromellitate).
Silver salts of aliphatic carboxylic acids containing a thioether group as described in U.S. Pat. No. 3,330,663 (Weyde et al.) are also useful. Soluble silver carboxylates comprising hydrocarbon chains incorporating ether or thioether linkages, or sterically hindered substitution in the xcex1- (on a hydrocarbon group) or ortho- (on an aromatic group) position, and displaying increased solubility in coating solvents and affording coatings with less light scattering can also be used. Such silver carboxylates are described in U.S. Pat. No. 5,491,059 (Whitcomb). Mixtures of any of the silver salts described herein can also be used if desired.
Silver salts of sulfonates are also useful in the practice of this invention. Such materials are described for example in U.S. Pat. No. 4,504,575 (Lee). Silver salts of sulfosuccinates are also useful as described for example in EP-A-0 227 141 (Leenders et al.).
Moreover, silver salts of acetylenes can also be used as described, for example in U.S. Pat. No. 4,761,361 (Ozaki et al.) and U.S. Pat. No. 4,775,613 (Hirai et al.).
The methods used for making silver soap emulsions are well known in the art and are disclosed in Research Disclosure, April 1983, Item 22812, Research Disclosure, October 1983, Item 23419, U.S. Pat. No. 3,985,565 (Gabrielsen et al.) and the references cited above.
Non-photosensitive sources of reducible silver ions can also be provided as core-shell silver salts such as those described in commonly assigned and copending U.S. Pat. No. 6,355,408 (Whitcomb et al.), that is incorporated herein by reference. These silver salts include a core comprised of one or more silver salts and a shell having one or more different silver salts.
Still another useful source of non-photosensitive reducible silver ions in the practice of this invention are the silver dimer compounds that comprise two different silver salts as described in copending U.S. Ser. No. 09/812,597 (filed Mar. 20, 2001 by Whitcomb), that is incorporated herein by reference. Such non-photosensitive silver dimer compounds comprise two different silver salts, provided that when the two different silver salts comprise straight-chain, saturated hydrocarbon groups as the silver coordinating ligands, those ligands differ by at least 6 carbon atoms.
As one skilled in the art would understand, the non-photosensitive source of reducible silver ions can include various mixtures of the various silver salt compounds described herein, in any desirable proportions.
The photosensitive silver halide and the non-photosensitive source of reducible silver ions must be in catalytic proximity (that is, reactive association). It is preferred that these reactive components be present in the same emulsion layer.
The one or more non-photosensitive sources of reducible silver ions are preferably present in an amount of about 5% by weight to about 70% by weight, and more preferably, about 10% to about 50% by weight, based on the total dry weight of the emulsion layers. Stated another way, the amount of the sources of reducible silver ions is generally present in an amount of from about 0.001 to about 0.2 mol/m2 of the dry photothermographic material, and preferably from about 0.01 to about 0.05 mol/m2 of that material.
The total amount of silver (from all silver sources) in the photothermographic materials is generally at least 0.002 mol/m2 and preferably from about 0.01 to about 0.05 mol/m2.
The reducing agent (or reducing agent composition comprising two or more components) for the source of reducible silver ions can be any material, preferably an organic material, that can reduce silver (I) ion to metallic silver. Conventional photographic developing agents such as methyl gallate, hydroquinone, substituted hydroquinones, 3-pyrazolidinones, p-aminophenols, p-phenylenediamines, hindered phenols, amidoximes, azines, catechol, pyrogallol, ascorbic acid (or derivatives thereof), leuco dyes and other materials readily apparent to one skilled in the art can be used in this manner as described for example in U.S. Pat. No. 6,020,117 (Bauer et al.).
An xe2x80x9cascorbic acid reducing agentxe2x80x9d (also referred to as a developer or developing agent) means ascorbic acid, and complexes and derivatives thereof Ascorbic acid developing agents are described in a considerable number of publications in photographic processes, including U.S. Pat. No. 5,236,816 (Purol et al.) and references cited therein. Useful ascorbic acid developing agents include ascorbic acid and the analogues, isomers and derivatives thereof. Such compounds include, but are not limited to, D- or L-ascorbic acid, sugar-type derivatives thereof (such as sorboascorbic acid, xcex3-lactoascorbic acid, 6-desoxy-L-ascorbic acid, L-rhamnoascorbic acid, imino-6-desoxy-L-ascorbic acid, glucoascorbic acid, fucoascorbic acid, glucoheptoascorbic acid, maltoascorbic acid, L-arabosascorbic acid), sodium ascorbate, potassium ascorbate, isoascorbic acid (or L-erythroascorbic acid), and salts thereof (such as alkali metal, ammonium or others known in the art), endiol type ascorbic acid, an enaminol type ascorbic acid, a thioenol type ascorbic acid, and an enamin-thiol type ascorbic acid, as described for example in U.S. Pat. No. 5,498,511 (Yamashita et al.), EP-A-0 585,792 (Passarella et al.), EP-A-0 573 700 (Lingier et al.), EP-A-0 588 408 (Hieronymus et al.), U.S. Pat. No. 5,089,819 (Knapp), U.S. Pat. No. 5,278,035 (Knapp), U.S. Pat. No. 5,384,232 (Bishop et al.), U.S. Pat. No. 5,376,510 (Parker et al.), JP 7-56286 (Toyoda), U.S. Pat. No. 2,688,549 (James et al.), and Research Disclosure, March 1995, Item 37152. D-, L-, or D,L-ascorbic acid (and alkali metal salts thereof) or isoascorbic acid (or alkali metal salts thereof) are preferred. Sodium ascorbate and sodium isoascorbate are preferred salts. Mixtures of these developing agents can be used if desired.
Hindered phenol reducing agents can also be used (alone or in combination with one or more high-contrast co-developing agents and co-developer contrast enhancing agents). Hindered phenols are compounds that contain only one hydroxy group on a given phenyl ring and have at least one additional substituent located ortho to the hydroxy group. Hindered phenol developers may contain more than one hydroxy group as long as each hydroxy group is located on different phenyl rings. Hindered phenol developers include, for example, binaphthols (that is, dihydroxybinaphthyls), biphenols (that is, dihydroxybiphenyls), bis(hydroxynaphthyl)methanes, bis(hydroxyphenyl)methanes (that is, bisphenols), hindered phenols, and hindered naphthols, each of which may be variously substituted.
Representative binaphthols include, but are not limited, to 1,1xe2x80x2-bi-2-naphthol, 1,1xe2x80x2-bi-4-methyl-2-naphthol and 6,6xe2x80x2-dibromo-bi-2-naphthol. For additional compounds see U.S. Pat. No. 3,094,417 (Workman) and U.S. Pat. No. 5,262,295 (Tanaka et al.), both incorporated herein by reference.
Representative biphenols include, but are not limited, to 2,2xe2x80x2-dihydroxy-3,3xe2x80x2-di-t-butyl-5,5-dimethylbiphenyl, 2,2xe2x80x2-dihydroxy-3,3xe2x80x2,5,5xe2x80x2-tetra-t-butylbiphenyl, 2,2xe2x80x2-dihydroxy-3,3xe2x80x2-di-t-butyl-5,5xe2x80x2-dichlorobiphenyl, 2-(2-hydroxy-3-t-butyl-5-methylphenyl)-4-methyl-6-n-hexylphenol, 4,4xe2x80x2-dihydroxy-3,3xe2x80x2,5,5xe2x80x2-tetra-t-butylbiphenyl and 4,4xe2x80x2-dihydroxy-3,3xe2x80x2,5,5xe2x80x2-tetramethylbiphenyl. For additional compounds see U.S. Pat. No. 5,262,295 (noted above).
Representative bis(hydroxynaphthyl)methanes include, but are not limited to, 4,4xe2x80x2-methylenebis(2-methyl-1-naphthol). For additional compounds see U.S. Pat. No. 5,262,295 (noted above).
Representative bis(hydroxyphenyl)methanes include, but are not limited to, bis(2-hydroxy-3-t-butyl-5-methylphenyl)methane (CAO-5), 1,1xe2x80x2-bis(2-hydroxy-3,5-dimethylphenyl)-3,5,5-trimethylhexane (NONOX or PERMANAX WSO), 1,1xe2x80x2-bis(3,5-di-t-butyl-4-hydroxypbenyl)methane, 2,2xe2x80x2-bis(4-hydroxy-3-methylphenyl)propane, 4,4xe2x80x2-ethylidene-bis(2-t-butyl-6-methylphenol), 2,2xe2x80x2-isobutylidene-bis(4,6-dimethylphenol) (LOWINOX 221B46), and 2,2xe2x80x2-bis(3,5-dimethyl-4-hydroxyphenyl)propane. For additional compounds see U.S. Pat. No. 5,262,295 (noted above).
Representative hindered phenols include, but are not limited to, 2,6-di-t-butylphenol, 2,6-di-t-butyl-4-methylphenol, 2,4-di-t-butylphenol, 2,6-dichlorophenol, 2,6-dimethylphenol and 2-t-butyl-6-methylphenol.
Representative hindered naphthols include, but are not limited to, 1-naphthol, 4-methyl-1-naphthol, 4-methoxy-1-naphthol, 4-chloro-1-naphthol and 2-methyl-1-naphthol. For additional compounds see U.S. Pat. No. 5,262,295 (noted above).
More specific alternative reducing agents that have been disclosed in dry silver systems including amidoximes such as phenylamidoxime, 2-thienylamidoxime and p-phenoxyphenylamidoxime, azines (for example, 4-hydroxy-3,5-dimethoxybenzaldehydrazine), a combination of aliphatic carboxylic acid aryl hydrazides and ascorbic acid [such as 2,2xe2x80x2-bis(hydroxymethyl)-propionyl-xcex2phenyl hydrazide in combination with ascorbic acid], a combination of polyhydroxybenzene and hydroxylamine, a reductone and/or a hydrazine [for example, a combination of hydroquinone and bis(ethoxyethyl)hydroxylamine], piperidinohexose reductone or formyl-4-methylphenylhydrazine, hydroxamic acids (such as phenylhydroxamic acid, p-bydroxyphenylhydroxamic acid, and o-alaninehydroxamic acid), a combination of azines and sulfonamidophenols (for example, phenothiazine and 2,6-dichloro-4-benzenesulfonamidophenol), xcex1-cyanophenylacetic acid derivatives (such as ethyl xcex1-cyano-2-methylphenylacetate and ethyl xcex1-cyanophenylacetate), bis-o-naphthols [such as 2,2xe2x80x2-dihydroxyl-1-binaphthyl, 6,6xe2x80x2-dibromo-2,2xe2x80x2-dihydroxy-1,1xe2x80x2-binaphthyl, and bis(2-hydroxy-1-naphthyl)methane], a combination of bis-o-naphthol and a 1,3-dihydroxybenzene derivative (for exanple, 2,4-dihydroxybenzophenone or 2,4-dihydroxyacetophenone), 5-pyrazolones such as 3-methyl-1-phenyl-5-pyrazolone, reductones (such as dimethylaminohexose reductone, anhydrodihydro-aminohexose reductone and anhydrodihydro-piperidone-hexose reductone), sulfonamidophenol reducing agents (such as 2,6-dichloro-4-benzenesulfonamido-phenol, and p-benzenesulfonamidophenol), indane-1,3-diones (such as 2-phenylindane-1,3-dione), chromans (such as 2,2-dimethyl-7-t-butyl-6-hydroxychroman), 1,4-dihydropyridines (such as 2,6-dimethoxy-3,5-dicarbethoxy-1,4-dihydropyridine), ascorbic acid derivatives (such as 1-ascorbylpalmitate, ascorbylstearate), and unsaturated aldehydes, ketones, and 3-pyrazolidones.
An additional class of reducing agents that can be used as developers are substituted hydrazines including the sulfonyl hydrazides described in U.S. Pat. No. 5,464,738 (Lynch et al.). Still other useful reducing agents are described, for example, in U.S. Pat. No. 3,074,809 (Owen), U.S. Pat. No. 3,094,417 (Workman), U.S. Pat. No. 3,080,254 (Grant, Jr.) and U.S. Pat. No. 3,887,417 (Klein et al.). Auxiliary reducing agents may be useful as described in U.S. Pat. No. 5,981,151 (Leenders et al.). All of these patents are incorporated herein by reference.
In some instances, the reducing agent composition comprises two or more components such as a hindered phenol developer and a co-developer that can be chosen from the various classes of reducing agents described below. Ternary developer mixtures involving the further addition of contrast enhancing agents are also useful. Such contrast enhancing agents can be chosen from the various classes of reducing agents described below.
Additional classes of reducing agents that can be used as co-developers are trityl hydrazides and formyl phenyl hydrazides as described in U.S. Pat. No. 5,496,695 (Simpson et al.), incorporated herein by reference.
Various contrast enhancing agents can be used in some photothermographic materials with specific co-developers. Examples of useful contrast enhancers include, but are not limited to, hydroxylamines (including hydroxylamine and alkyl- and aryl-substituted derivatives thereof), alkanolamines and ammonium phthalamate compounds as described for example, in U.S. Pat. No. 5,545,505 (Simpson), hydroxamic acid compounds as described for example, in U.S. Pat. No. 5,545,507 (Simpson et al.), N-acylhydrazine compounds as described for example, in U.S. Pat. No. 5,558,983 (Simpson et al.), and hydrogen atom donor compounds as described in U.S. Pat. No. 5,637,449 (Harring et al.). All of the patents above are incorporated herein by reference.
It is to be understood that not all combinations of developer and non-photosensitive source of reducible silver ions work equally well. One preferred combination includes a silver salt of benzotriazole, substituted derivatives thereof, or mixtures of such silver salts as the non-photosensitive source of reducible silver ions and an ascorbic acid reducing agent.
Another combination includes a silver fatty acid carboxylate having 10 to 30 carbon atoms, or mixtures of said silver carboxylates as the non-photosensitive source of reducible silver ions and a hindered phenol as the reducing agent.
The reducing agent (or mixture thereof) described herein is generally present as 1 to 10% (dry weight) of the emulsion layer. In multilayer constructions, if the reducing agent is added to a layer other than an emulsion layer, slightly higher proportions, of from about 2 to 15 weight % may be more desirable. Any co-developers may be present generally in an amount of from about 0.001% to about 1.5% (dry weight) of the emulsion layer coating.
The photothermographic materials of the invention can also contain other additives such as shelf-life stabilizers, antifoggants, contrast enhancing agents, toners, development accelerators, acutance dyes, post-processing stabilizers or stabilizer precursors, toners, thermal solvents (also known as xe2x80x9cmelt formersxe2x80x9d), and other image-modifying agents as would be readily apparent to one skilled in the art.
To further control the properties of photothermographic materials, (for example, contrast, Dmin, speed, or fog), it may be preferable to add one or more heteroaromatic mercapto compounds or heteroaromatic disulfide compounds of the formulae Arxe2x80x94Sxe2x80x94M1 and Arxe2x80x94Sxe2x80x94Sxe2x80x94Ar, wherein M1 represents a hydrogen atom or an alkali metal atom and Ar represents a heteroaromatic ring or fused heteroaromatic ring containing one or more of nitrogen, sulfur, oxygen, selenium, or tellurium atoms. Preferably, the heteroaromatic ring comprises benzimidazole, naphthimidazole, benzothiazole, naphthothiazole, benzoxazole, naphthoxazole, benzoselenazole, benzotellurazole, imidazole, oxazole, pyrazole, triazole, thiazole, thiadiazole, tetrazole, triazine, pyrimidine, pyridazine, pyrazine, pyridine, purine, quinoline, or quinazolinone. Compounds having other heteroaromatic rings and compounds providing enhanced sensitization at other wavelengths are also envisioned to be suitable. For example, heteroaromatic mercapto compounds are described as supersensitizers for infrared photothermographic materials in EP-A-0 559 228 (Philip Jr. et al.).
The photothermographic materials of the present invention can be further protected against the production of fog and can be stabilized against loss of sensitivity during storage. While not necessary for the practice of the invention, it may be advantageous to add mercury (II) salts to the emulsion layer(s) as an antifoggant. Preferred mercury (II) salts for this purpose are mercuric acetate and mercuric bromide. Other useful mercury salts include those described in U.S. Pat. No. 2,728,663 (Allen).
Other suitable antifoggants and stabilizers that can be used alone or in combination include thiazolium salts as described in U.S. Pat. No. 2,131,038 (Staud) and U.S. Pat. No. 2,694,716 (Allen), azaindenes as described in U.S. Pat. No. 2,886,437 (Piper), triazaindolizines as described in U.S. Pat. No. 2,444,605 (Heimbach), the urazoles described in U.S. Pat. No. 3,287,135 (Anderson), sulfocatechols as described in U.S. Pat. No. 3,235,652 (Kennard), the oximes described in GB 623,448 (Carrol et al.), polyvalent metal salts as described in U.S. Pat. No. 2,839,405 (Jones), thiuronium salts as described in U.S. Pat. No. 3,220,839 (Herz), palladium, platinum, and gold salts as described in U.S. Pat. No. 2,566,263 (Trirelli) and U.S. Pat. No. 2,597,915 (Damshroder), compounds having xe2x80x94SO2CBr3 groups as described for example in U.S. Pat. No. 5,594,143 (Kirk et al.) and U.S. Pat. No. 5,374,514 (Kirk et al.), and 2-(tribromomethylsulfonyl)quinoline compounds as described in U.S. Pat. No. 5,460,938 (Kirk et al.).
Stabilizer precursor compounds capable of releasing stabilizers upon application of heat during development can also be used. Such precursor compounds are described in for example, U.S. Pat. No. 5,158,866 (Simpson et al.), U.S. Pat. No. 5,175,081 (Krepski et al.), U.S. Pat. No. 5,298,390 (Sakizadeh et al.), and U.S. Pat. No. 5,300,420 (Kenney et al.).
In addition, certain substituted-sulfonyl derivatives of benzotriazoles (for example alkylsulfonylbenzotriazoles and arylsulfonylbenzotriazoles) have been found to be useful stabilizing compounds (such as for post-processing print stabilizing), as described in U.S. Pat. No. 6,171,767 (Kong et al.).
Furthermore, other specific useful antifoggants/stabilizers are described in more detail in U.S. Pat. No. 6,083,681 (Lynch et al.), incorporated herein by reference.
The photothermographic materials may also include one or more polyhalo antifoggants that include one or more polyhalo substituents including but not limited to, dichloro, dibromo, trichloro, and tribromo groups. The antifoggants can be aliphatic, alicyclic, or aromatic compounds, including aromatic heterocyclic and carbocyclic compounds.
Particularly useful antifoggants of this type are polyhalo antifoggants, such as those having a xe2x80x94SO2C(Xxe2x80x2)3 group wherein Xxe2x80x2 represents the same or different halogen atoms.
Another class of useful antifoggants are those described in copending and commonly assigned U.S. Ser. No. 10/014,961 (filed Dec. 11, 2001 by Burgmaier and Klaus), incorporated herein by reference. These compounds are generally defined as compounds having a pKa of 8 or less and represented by the following Structure I:
R1xe2x80x94SO2xe2x80x94C(R2)R3xe2x80x94(CO)mxe2x80x94(L1)nxe2x80x94SGxe2x80x83xe2x80x83(I)
wherein R1 is an aliphatic or cyclic group, R2 and R3 are independently hydrogen or bromine as long as at least one of them is bromine, L1 is an aliphatic divalent linking group, m and n are independently 0 or 1, and SG is a solubilizing group having a pKa of 8 or less.
In some preferred embodiments, the antifoggants are defined using Structure I noted above wherein:
when m and n are both 0, SG is carboxy (or a salt thereof), sulfo (or a salt thereof), phospho (or a salt thereof), (xe2x80x94SO2Nxe2x88x92COR4)(M2)+, or (xe2x80x94Nxe2x88x92SO2R4)(M2)+,
when m is 1 and n is 0, SG is carboxy (or salt thereof), sulfo (or a salt thereof), phospho (or a salt thereof), or (xe2x80x94Nxe2x88x92SO2R4)(M2)+,
when m and n are both 1, SG is carboxy (or a salt thereof), sulfo (or a salt thereof), phospho (or a salt thereof), or (xe2x80x94SO2Nxe2x88x92COR4)(M2)+, and R4 is an aliphatic or cyclic group, and (M2)+ is a cation other than a proton.
Advantageously, the photothermographic materials of this invention also include one or more xe2x80x9cthermal solventsxe2x80x9d also called xe2x80x9cheat solvents,xe2x80x9d xe2x80x9cthermosolvents,xe2x80x9d xe2x80x9cmelt formers,xe2x80x9d xe2x80x9cwaxes,xe2x80x9d or xe2x80x9cplasticizersxe2x80x9d for improving the reaction speed of the silver-developing redox-reaction at elevated temperature.
By the term xe2x80x9cthermal solventxe2x80x9d in this invention is meant an organic material which becomes a plasticizer or liquid solvent for at least one of the imaging layers upon heating at a temperature above 60xc2x0 C. Useful for that purpose are a polyethylene glycol having a mean molecular weight in the range of 1,500 to 20,000 described in U.S. Pat. No. 3,347,675. Further are mentioned compounds such as urea, methyl sulfonamide and ethylene carbonate being thermal solvents described in U.S. Pat. No. 3,667,959, and compounds such as tetrahydro-thiophene-1,1-dioxide, methyl anisate and 1,10-decanediol being described as thermal solvents in Research Disclosure, December 1976, Item 15027, pages 26-28. Other representative examples of such compounds include, but are not limited to, salicylanilide, phthalimide, N-hydroxyphthalimide, N-potassium-phthalimide, succinimide, N-hydroxy-1,8-naphthalimide, phthalazine, 1-(2H)-phthalazinone, nicotinamide, 2-acetylphthalazinone, benzanilide, dimethylurea, D-sorbitol, and benzenesulfonamide. Combinations of these compounds can also be used including a combination of succinimide and dimethylurea. Still other examples of thermal solvents have been described in U.S. Pat. No. 3,438,776 (Yudelson), U.S. Pat. No. 4,473,631 (Hiroyuki et al.), U.S. Pat. No. 4,740,446 (Schranz et al.), U.S. Pat. No. 6,013,420 (Windender), U.S. Pat. No. 5,368,979 (Freedman et al.), 5,716,772 (Taguchi et al.), and U.S. Pat. No. 5,250,386 (Aono et al.), and in published EP-A 0 119 615 (Nakamura et al.) and U.S. Pat. No. 0,122,512 (Aono et al.), all incorporated herein by reference.
xe2x80x9cTonersxe2x80x9d are compounds that improve image color and increase the optical density of the developed image. For black and white photothermographic films, particularly useful toners are those that also contribute to the formation of a black image upon development. Thus, the use of xe2x80x9ctonersxe2x80x9d or derivatives thereof is highly desirable and toners are preferably included in the photothermographic materials described herein. Such compounds are well known materials in the photothermographic art, as described in U.S. Pat. No. 3,080,254 (Grant, Jr.), U.S. Pat. No. 3,847,612 (Winslow), U.S. Pat. No. 4,123,282 (Winslow), U.S. Pat. No. 4,082,901 (Laridon et al.), U.S. Pat. No. 3,074,809 (Owen), U.S. Pat. No. 3,446,648 (Workman), U.S. Pat. No. 3,844,797 (Willems et al.), U.S. Pat. No. 3,951,660 (Hagemann et al.), U.S. Pat. No. 5,599,647 (Defieuw et al.), U.S. Pat. No. 4,220,709 (deMauriac et al.), U.S. Pat. No. 4,451,561 (Hirabayashi et al.), U.S. Pat. No. 4,543,309 (Hirabayashi et al.), U.S. Pat. No. 3,832, i 86 (Masuda et al.), U.S. Pat. No. 4,201,582 (White et al.), U.S. Pat. No. 3,881,938 (Masuda et al.), and GB 1,439,478 (AGFA).
Examples of toners include, but are not limited to, phthalimide and N-hydroxyphthalimide, cyclic imides (such as succinimide), pyrazoline-5-ones, quinazolinone, 1-phenylurazole, 3-phenyl-2-pyrazoline-5-one, and 2,4-thiazolidinedione, naphthalimides (such as N-hydroxy-1,8-naphthalimide), cobalt complexes [such as hexaaminecobalt(3+) trifluoroacetate], mercaptans (such as mercaptotriazoles including 3-mercapto-1,2,4-triazole, 3-mercapto-4-phenyl-1,2,4-triazole, 4-phenyl-1,2,4-triazolidine-3,5-dithione, 4-allyl-3-amino-5-mercapto-1,2,4-triazole and 4-methyl-5-thioxo-1,2,4-triazolidin-3-one, pyrimides including 2,4-dimercaptopyrimidine, thiadiazoles including 2,5-dimercapto-1,3,4-thiadiazole, 5-methyl-1,3,4-thiadiazolyl-2-thiol, mercaptotetrazoles including 1-phenyl-5-mercaptotetrazole, and 5-acetylamino-1,3,4-thiadiazoline-2-thione, mercaptoimidazoles including 1,3-dihydro-1-phenyl-2H-Imidazole-2-thione,), N-(aminomethyl)aryldicarboximides [such as (N,N-dimethylaminomethyl)phthalimide, and N-(dimethylaminomethyl)naphthalene-2,3-dicarboximide], a combination of blocked pyrazoles, isothiuronium derivatives, and certain photobleach agents [such as a combination of N,Nxe2x80x2-hexamethylene-bis(1-carbamoyl-3,5-dimethylpyrazole), 1,8-(3,6-diaza-octane)bis(isothiuronium)trifluoroacetate, and 2-(tribromomethylsulfonyl benzothiazole)], merocyanine dyes {such as 3-ethyl-5-[(3-ethyl-2-benzothiazolinylidene)-1-methyl-ethylidene]-2-thio-2,4-o-azolidinedione}, phthalazine and derivatives thereof [such as those described in U.S. Pat. No. 6,146,822 (Asanuma et al.)], phthalazinone and phthalazinone derivatives, or metal salts or these derivatives [such as 4-(1-naphthyl)phthalazinone, 6-chlorophthalazinone, 5,7-dimethoxyphthalazinone, and 2,3-dihydro-1,4-phthalazinedione], a combination of phthalazine (or derivative thereof) plus one or more phthalic acid derivatives (such as phthalic acid, 4-methylphthalic acid, 4-nitrophthalic acid, and tetrachlorophtbalic anhydride), quinazolinediones, benzoxazine or napbthoxazine derivatives, rhodium complexes functioning not only as tone modifiers but also as sources of halide ion for silver halide formation in-situ [such as ammonium hexachlororhodate (III), rhodium bromide, rhodium nitrate, and potassium hexachlororhodate (III)], benzoxazine-2,4-diones (such as 1,3-benzoxazine-2,4-dione, 8-methyl-1,3-benzoxazine-2,4-dione and 6-nitro-1,3-benzoxazine-2,4-dione), pyrimidines and asym-triazines (such as 2,4-dihydroxypyrimidine, 2-hydroxy-4-aminopyrimidine and azauracil) and tetraazapentalene derivatives [such as 3,6-dimercapto-1,4-diphenyl-1H,4H-2,3a,5,6a-tetraazapentalene and 1,4-di-(o-chlorophenyl)-3,6-dimercapto-1H,4H-2,3a,5,6a-tetraazapentalene].
Phthalazine and phthalazine derivatives [such as those described in U.S. Pat. No. 6,146,822 (noted above), incorporated herein by reference] are particularly useful as toners in when using silver carboxylate compounds as the non-photosensitive source of reducible silver and hindered phenols as developers. Phthalazine and derivatives thereof can be used in any layer of the photothermographic material on either side of the support.
Compounds that are particularly useful as toners in the practice of this invention when using silver salts of nitrogen-containing heterocyclic compounds containing an imino group as the non-photosensitive source of reducible silver and ascorbic acid, an ascorbic acid complex or an ascorbic acid derivative as a reducing agent are mercaptotriazole compounds defined by the following Structure II 
wherein R1 and R2 independently represent hydrogen, a substituted or unsubstituted alkyl group of from 1 to 7 carbon atoms (such as methyl, ethyl, isopropyl, t-butyl, n-hexyl, hydroxymethyl, and benzyl), a substituted or unsubstituted alkenyl group having 2 to 5 carbon atoms in the hydrocarbon chain (such as ethenyl, 1,2-propenyl, methallyl, and 3-buten-1-yl), a substituted or unsubstituted cycloalkyl group having 5 to 7 carbon atoms forming the ring (such as cyclopenyl, cyclohexyl, and 2,3-dimethylcyclohexyl), a substituted or unsubstituted aromatic or non-aromatic heterocyclyl group having 5 or 6 carbon, nitrogen, oxygen, or sulfur atoms forming the aromatic or non-aromatic heterocyclyl group (such as pyridyl, furanyl, thiazolyl, and thienyl), an amino or amide group (such as amino or acetamido), and a substituted or unsubstituted aryl group having 6 to 10 carbon atoms forming the aromatic ring (such as phenyl, tolyl, naphthyl, and 4-ethoxyphenyl).
In addition, R2 and R2 can be a substituted or unsubstituted Y1xe2x80x94(CH2)kxe2x80x94 group wherein Y1 is a substituted or unsubstituted aryl group having 6 to 10 carbon atoms as defined above for R1 and R2, or a substituted or unsubstituted aromatic or non-aromatic heterocyclyl group as defined above for R1,. Also, k is 1-3.
Alternatively, R1 and R2 taken together can form a substituted or unsubstituted, saturated or unsaturated 5- to 7-membered aromatic or non-aromatic nitrogen-containing heterocyclic ring comprising carbon, nitrogen, oxygen, or sulfur atoms in the ring (such as pyridyl, diazinyl, triazinyl, piperidine, morpholine, pyrrolidine, pyrazolidine, and thiomorpholine).
Still again, R1 or R2 can represent a divalent linking group (such as a phenylene, methylene, or ethylene group) linking two mercaptotriazole groups, and R2 may further represent carboxy or its salts.
M1 is hydrogen or a monovalent cation (such as an alkali metal cation, an ammonium ion, or a pyridinium ion).
The definition of mercaptotriazoles of Structure II also includes the following provisos:
1) R1 and R2 are not simultaneously hydrogen.
2) When R1 is substituted or unsubstituted phenyl or benzyl, R2 is not substituted or unsubstituted phenyl or benzyl.
3) When R2 is hydrogen, R1 is not allenyl, 2,2-diphenylethyl, xcex1-methylbenzyl, or a phenyl group having a cyano or a sulfonic acid substituent.
4) When R1 is benzyl or phenyl, R2 is not substituted 1,2-dihydroxyethyl, or 2-hydroxy-2-propyl.
5) When R1 is hydrogen, R2 is not 3-phenylthiopropyl.
In one further optional embodiment, the photothermographic material is further defined wherein:
6) One or more thermally developable imaging layers has a pH less than 7.
Preferably, R1 is methyl, t-butyl, a substituted phenyl or benzyl group. More preferably R1 is benzyl. Also, R1 can represent a divalent linking group (such as a phenylene, methylene, or ethylene group) that links two mercaptotriazole groups.
Preferably, R2 is hydrogen, acetamido, or hydroxymethyl. More preferably, R2 is hydrogen. Also, R2 can represent a divalent linking group (such as a phenylene, methylene, or ethylene group) that links two mercaptotriazole groups.
As noted above, in one embodiment, one or more thermally developable imaging layers has a pH less than 7. The pH of these layers may be conveniently controlled to be acidic by addition of ascorbic acid as the developer. Alternatively, the pH may be controlled by adjusting the pH of the silver salt dispersion prior to coating with mineral acids such as, for example, sulfuric acid or nitric acid or by addition of organic acids such as citric acid. It is preferred that the pH of the one or more imaging layers be less than 7 and preferably less than 6. This pH value can be determined using a surface pH electrode after placing a drop of KNO3 solution on the sample surface. Such electrodes are available from Corning (Corning, N.Y.).
Many of the toners described herein are heterocyclic compounds. It is well known that heterocyclic compounds exist in tautomeric forms. In addition both annular (ring) tautomerism and substituent tautomerism are often possible.
For example, in one preferred class of toners, 1,2,4-mercaptotriazole compounds, at least three tautomers (a 1H form, a 2H form, and a 4H form) are possible. 
In addition, 1,2,4-mercaptotriazoles are also capable of thiol-thione substituent tautomerism. 
Interconversion among these tautomers can occur rapidly and individual tautomers cannot be isolated, although one tautomeric form may predominate. For the 1,2,4-mercaptotriazoles described herein, the 4H-thiol structural formalism is used with the understanding that such tautomers do exist.
Mercaptotriazole compounds represented by Structure II are particularly preferred when used with silver benzotriazole as the non-photosensitive source of reducible silver and ascorbic acid as the reducing agent. When so used, compounds represented by Structure II have been found to give dense black images,
Representative compounds having Structure II and useful as toners in the practice of the present invention include the following compounds T-1 through T-59: 
Compounds T-1, T-2, T-3, T-11, T-12, T-16, T-37, T-41, and T-44, are preferred in the practice of this invention, and Compounds T-1, T-2, and T-3 are most preferred.
The mercaptotriazole toners described herein can be readily prepared using well known synthetic methods. For example, compound T-1 can be prepared as described in U.S. Pat. No. 4,628,059 (Finkelstein et al.). Additional preparations of various mercaptotraizoles are described in U.S. Pat. No. 3,769,411 (Greenfield et al.), U.S. Pat. No. 4,183,925 (Baxter et al.), U.S. Pat. No. 6,074,813 (Asanuma et al.), DE 1 670 604 (Korosi), and in Chem. Abstr. 1968, 69, 52114j. Some mercaptotriazole compounds are commercially available.
As would be understood by one skilled in the art, two or more mercaptotriazole toners as defined by Structure II can be used in the practice of this invention if desired, and the multiple toners can be located in the same or different layers of the photothermographic materials.
Additional conventional toners can also be included with the one or more mercaptotriazoles described above. Such compounds are well known materials in the photothermographic art, as shown in U.S. Pat. No. 3,080,254 (Grant, Jr.), U.S. Pat. No. 3,847,612 (Winslow), U.S. Pat. No. 4,123,282 (Winslow), U.S. Pat. No. 4,082,901 (Laridon et al.), U.S. Pat. No. 3,074,809 (Owen), U.S. Pat. 3,446,648 (Workman), U.S. Pat. No. 3,844,797 (Willems et al.), U.S. Pat. No. 3,951,660 (Hagemann et al.), U.S. Pat. No. 5,599,647 (Defieuw et al.) and GB 1,439,478 (AGFA).
Mixtures of mercaptotriazoles with additional toners (for example, 3-mercapto-4-benzyl-1,2,4-triazole with phthalazine) are also useful in the practice of this invention.
Generally, one or more toners described herein are present in an amount of about 0.01% by weight to about 10%, and more preferably about 0.1% by weight to about 10% by weight, based on the total dry weight of the layer in which it is included. Toners may be incorporated in one or more of the thermally developable imaging layers as well as in adjacent layers such as a protective overcoat or underlying xe2x80x9ccarrierxe2x80x9d layer. The toners can be located on both sides of the support if thermally developable imaging layers are present on both sides of the support.
The tabular grain photosensitive silver halide, the non-photo-sensitive source of reducible silver ions, the reducing agent composition, toner(s), and any other additives used in the present invention are generally added to one or more hydrophilic binders. Thus, predominantly aqueous formulations (at least 50 solvent volume % and preferably at least 70 solvent volume % is water) are used to prepare the photothermographic materials of this invention. Mixtures of such binders can also be used.
Examples of useful hydrophilic binders include, but are not limited to, proteins and protein derivatives, gelatin and gelatin derivatives (hardened or unhardened, including alkali- and acid-treated gelatins, acetylated gelatin, oxidized gelatin, phthalated gelatin, and deionized gelatin), cellulosic materials such as hydroxymethyl cellulose and cellulosic esters, acrylamide/methacrylamide polymers, acrylic/methacrylic polymers polyvinyl pyrrolidones, polyvinyl alcohols, poly(vinyl lactams), polymers of sulfoalkyl acrylate or methacrylates, hydrolyzed polyvinyl acetates, polyacrylamides, polysaccharides (such as dextrans and starch ethers), and other synthetic or naturally occurring vehicles commonly known for use in aqueous-based photographic emulsions (see for example, Research Disclosure, Item 38957, noted above). Cationic starches can be also be used as a peptizer for tabular silver halide grains as described in U.S. Pat. No. 5,620,840 (Maskasky) and U.S. Pat. No. 5,667,955 (Maskasky).
Particularly useful hydrophilic binders are gelatin, gelatin derivatives, polyvinyl alcohols, and cellulosic materials. Gelatin and its derivatives are most preferred, and comprise at least 75 weight % of total binders when a mixture of binders is used.
xe2x80x9cMinorxe2x80x9d amounts of hydrophobic binders can also be present as long as more than 50% (by weight of total binders) is composed of hydrophilic binders. Examples of typical hydrophobic binders include, but are not limited to, polyvinyl acetals, polyvinyl chloride, polyvinyl acetate, cellulose acetate, cellulose acetate butyrate, polyolefins, polyesters, polystyrenes, polyacrylonitrile, polycarbonates, methacrylate copolymers, maleic anhydride ester copolymers, butadiene-styrene copolymers, and other materials readily apparent to one skilled in the art. Copolymers (including terpolymers) are also included in the definition of polymers. The polyvinyl acetals (such as polyvinyl butyral and polyvinyl formal) and vinyl copolymers (such as polyvinyl acetate and polyvinyl chloride) are particularly preferred. Particularly suitable binders are polyvinyl butyral resins that are available as BUTVAR(copyright) B79 (Solutia, Inc.) and PIOLOFORM(copyright) BS-18 or PIOLOFORM(copyright) BL-16 (Wacker Chemical Company). Minor amounts of aqueous dispersions (such as latexes) of hydrophobic binders may also be used. Such latex binders are described, for example, in EP-0 911 691 A1 (Ishizaka et al.)
Hardeners for various binders may be present if desired and the hydrophilic binders used in the photothermographic materials are generally partially or fully hardened using any conventional hardener. Useful hardeners are well known and include vinyl sulfone compounds described, U.S. Pat. No. 6,143,487 (Philip et al.), EP 0 460 589 (Gathmann et al.), aldehydes, and various other hardeners described in U.S. Pat. No. 6,190,822 (Dickerson et al.), as well as those described in T. H. James, The Theory of the Photographic Process, Fourth Edition, Eastman Kodak Company, Rochester, N.Y., 1977, Chapter 2, pp. 77-8.
Where the proportions and activities of the photothermographic materials require a particular developing time and temperature, the binder(s) should be able to withstand those conditions. Generally, it is preferred that the binder does not decompose or lose its structural integrity at 150xc2x0 C. for 60 seconds. It is more preferred that the binder does not decompose or lose its structural integrity at 177xc2x0 C. for 60 seconds.
The polymer binder(s) is used in an amount sufficient to carry the components dispersed therein. The effective range can be appropriately determined by one skilled in the art. Preferably, a binder is used at a level of about 10% by weight to about 90% by weight, and more preferably at a level of about 20% by weight to about 70% by weight, based on the total dry weight of the layer in which it is included. The amount of binders in double-sided photothermographic materials can be the same or different.
The photothermographic materials of this invention comprise a polymeric support that is preferably a flexible, transparent film that has any desired thickness and is composed of one or more polymeric materials, depending upon their use. The supports are generally transparent (especially if the material is used as a photomask) or at least translucent, but in some instances, opaque supports may be useful. They are required to exhibit dimensional stability during thermal development and to have suitable adhesive properties with overlying layers. Useful polymeric materials for making such supports include, but are not limited to, polyesters (such as polyethylene terephthalate and polyethylene naphthalate), cellulose acetate and other cellulose esters, polyvinyl acetal, polyolefins (such as polyethylene and polypropylene), polycarbonates, and polystyrenes (and polymers of styrene derivatives). Preferred supports are composed of polymers having good heat stability, such as polyesters and polycarbonates. Support materials may also be treated or annealed to reduce shrinkage and promote dimensional stability. Polyethylene terephthalate film is a particularly preferred support. Various support materials are described, for example, in Research Disclosure, August 1979, Item 18431. A method of making dimensionally stable polyester films is described in Research Disclosure, September 1999, Item 42536.
It is also useful to use supports comprising dichroic mirror layers wherein the dichroic mirror layer reflects radiation at least having the predetermined range of wavelengths to the emulsion layer and transmits radiation having wavelengths outside the predetermined range of wavelengths. Such dichroic supports are described in U.S. Pat. No. 5,795,708 (Boutet), incorporated herien by reference.
It is further possible to use transparent, multilayer, polymeric supports comprising numerous alternating layers of at least two different polymeric materials. Such multilayer polymeric supports preferably reflect at least 50% of actinic radiation in the range of wavelengths to which the photothermographic sensitive material is sensitive, and provide photothermographic materials having increased speed. Such transparent, multilayer, polymeric supports are described in WO02/21208 A1 (Simpson et al.), incorporated herein by reference.
Opaque supports, such as dyed polymeric films and resin-coated papers that are stable to high temperatures, can also be used.
Support materials can contain various colorants, pigments, antihalation or acutance dyes if desired. Support materials may be treated using conventional procedures (such as corona discharge) to improve adhesion of overlying layers, or subbing or other adhesion-promoting layers can be used. Useful subbing layer formulations include those conventionally used for photographic materials such as vinylidene halide polymers.
An aqueous formulation for the photothermographic emulsion layer(s) can be prepared by dissolving and dispersing the hydrophilic binder (such as gelatin or a gelatin derivative), the photosensitive ultrathin tabular grain silver halide(s), the non-photosensitive source of reducible silver ions, the reducing agent composition, and optional addenda in water or water-organic solvent mixtures to provide aqueous-based coating formulations. Minor (less than 50 volume %) of water-miscible organic solvents such as water-miscible alcohols, acetone, or methyl ethyl ketone, may also be present. Preferably, the solvent system used to provide these formulations is at least 80 volume % water and more preferably the solvent system is at least 90 volume % water).
Photothermographic materials of this invention can contain plasticizers and lubricants such as polyalcohols and diols of the type described in U.S. Pat. No. 2,960,404 (Milton et al.), fatty acids or esters such as those described in U.S. Pat. No. 2,588,765 (Robijns) and U.S. Pat. No. 3,121,060 (Duane), and silicone resins such as those described in GB 955,061 (DuPont). The materials can also contain matting agents such as starch, titanium dioxide, zinc oxide, silica, and polymeric beads including beads of the type described in U.S. Pat. No. 2,992,101 (Jelley et al.) and U.S. Pat. No. 2,701,245 (Lynn). Polymeric fluorinated surfactants may also be useful in one or more layers of the photothermographic materials for various purposes, such as improving coatability and optical density uniformity as described in U.S. Pat. No. 5,468,603 (Kub).
EP-0 792 476 B1 (Geisler et al.) describes various means of modifying photothermographic materials to reduce what is known as the xe2x80x9cwoodgrainxe2x80x9d effect, or uneven optical density. This effect can be reduced or eliminated by several means, including treatment of the support, adding matting agents to the topcoat, using acutance dyes in certain layers or other procedures described in the noted publication.
The photothermographic materials of this invention can include antistatic or conducting layers. Such layers may contain soluble salts (for example, chlorides or nitrates), evaporated metal layers, or ionic polymers such as those described in U.S. Pat. No. 2,861,056 (Minsk) and U.S. Pat. No. 3,206,312. (Sterman et al.), or insoluble inorganic salts such as those described in U.S. Pat. No. 3,428,451 (Trevoy), electroconductive underlayers such as those described in U.S. Pat. No. 5,310,640 (Markin et al.), electronically-conductive metal antimonate particles such as those described in U.S. Pat. No. 5,368,995 (Christian et al.), and electrically-conductive metal-containing particles dispersed in a polymeric binder such as those described in EP-A-0 678 776 (Melpolder et al.). Other antistatic agents are well known in the art.
Other conductive compositions include one or more fluoro-chemicals each of which is a reaction product of Rfxe2x80x94CH2CH2xe2x80x94SO3H with an amine wherein Rf comprises 4 or more fully fluorinated carbon atoms. These antistatic compositions are described in more detail in copending U.S. Ser. No. 10/107,551 (filed Mar. 27, 2002 by Sakizadeh, LaBelle, Orem, and Bhave), that is incorporated herein by reference.
The photothermographic materials of this invention can be constructed of one or more layers on a support. Single layer materials should contain the tabular grain photosensitive silver halide, the non-photosensitive source of reducible silver ions, the reducing agent composition, the hydrophilic binder, as well as optional materials such as toners, acutance dyes, coating aids and other adjuvants.
Two-layer constructions comprising a single imaging layer coating containing all the ingredients and a surface protective topcoat are generally found in the materials of this invention. However, two-layer constructions containing photosensitive silver halide and non-photosensitive source of reducible silver ions in one imaging layer (usually the layer adjacent to the support) and the reducing agent composition and other ingredients in the second imaging layer or distributed between both layers are also envisioned.
For double-sided photothermographic materials, both sides of the support can include one or more of the same or different imaging layers, interlayers, and protective topcoat layers. In such materials preferably a topcoat is present as the outermost layer on both sides of the support. The thermally developable layers on opposite sides can have the same or different construction and can be overcoated with the same or different protective layers.
Layers to promote adhesion of one layer to another in photothermographic materials are also known, as described for example in U.S. Pat. No. 5,891,610 (Bauer et al.), U.S. Pat. No. 5,804,365 (Bauer et al.), and U.S. Pat. No. 4,741,992 (Przezdziecki). Adhesion can also be promoted using specific polymeric adhesive materials as described for example in U.S. Pat. No. 5,928,857 (Geisler et al.).
Layers to reduce emissions from the film may also be present, including the polymeric barrier layers described in U.S. Pat. No. 6,352,819 (Kenney et al.), U.S. Pat. No. 6,352,820 (Bauer et al.), and copending U.S. Ser. No. 09/916,366 (filed Jul. 27, 2001 by Bauer, Horch, Miller, Teegarden, Hunt, and Sakizadeh), all incorporated herein by reference.
Photothermographic formulations described herein can be coated by various coating procedures including wire wound rod coating, dip coating, air knife coating, curtain coating, slide coating, or extrusion coating using hoppers of the type described in U.S. Pat. No. 2,681,294 (Beguin). Layers can be coated one at a time, or two or more layers can be coated simultaneously by the procedures described in U.S. Pat. No. 2,761,791 (Russell), U.S. Pat. No. 4,001,024 (Dittman et al.), U.S. Pat. No. 4,569,863 (Keopke et al.), U.S. Pat. No. 5,340,613 (Hanzalik et al.), U.S. Pat. No. 5,405,740 (LaBelle), U.S. Pat. No. 5,415,993 (Hanzalik et al.), U.S. Pat. No. 5,525,376 (Leonard), U.S. Pat. No. 5,733,608 (Kessel et al.), U.S. Pat. No. 5,849,363 (Yapel et al.), U.S. Pat. No. 5,843,530 (Jerry et al.), U.S. Pat. No. 5,861,195 (Bhave et al.), and GB 837,095 (Ilford). A typical coating gap for the emulsion layer can be from about 10 to about 750 xcexcm, and the layer can be dried in forced air at a temperature of from about 20xc2x0 C. to about 100xc2x0 C. It is preferred that the thickness of the layer be selected to provide maximum image densities greater than about 0.2, and more preferably, from about 0.5 to 5.0 or more, as measured by a MacBeth Color Densitometer Model TD 504.
When the layers are coated simultaneously using various coating techniques, a xe2x80x9ccarrierxe2x80x9d layer formulation comprising a single-phase mixture of the two or more polymers described above may be used. Such formulations are described U.S. Pat. No. 6,355,405 (Ludemann et al.), incorporated herein by reference.
Mottle and other surface anomalies can be reduced in the materials of this invention by incorporation of a fluorinated polymer as described for example in U.S. Pat. No. 5,532,121 (Yonkoski et al.) or by using particular drying techniques as described, for example in U.S. Pat. No. 5,621,983 (Ludemann et al.).
Preferably, two or more layers are applied to a film support using slide coating. The first layer can be coated on top of the second layer while the second layer is still wet. The first and second fluids used to coat these layers can be the same or different.
While the first and second layers can be coated on one side of the film support, manufacturing methods can also include forming on the opposing or backside of said polymeric support, one or more additional layers, including an antihalation layer, an antistatic layer, or a layer containing a matting agent (such as silica), an imaging layer, a protective topcoat layer, or a combination of such layers.
In some embodiments, the photothermographic materials of this invention include a surface protective layer on the same side of the support as the one or more thermally developable layers, an antihalation layer on the opposite side of the support, or both a surface protective layer and an antihalation layer on their respective sides of the support.
It is also contemplated that the photothermographic materials of this invention can include thermally developable imaging (or emulsion) layers on both sides of the support and at least one infrared radiation absorbing heat-bleachable composition in an antihalation underlayer beneath other layers on one or both sides of the support.
To promote image sharpness, photothermographic materials according to the present invention can contain one or more layers containing acutance, filter, cross-over prevention (anti-crossover), anti-irradiation, and/or antihalation dyes. These dyes are chosen to have absorption close to the exposure wavelength and are designed to absorb scattered light. One or more antihalation dyes may be incorporated into one or more antihalation layers according to known techniques, as an antihalation backing layer, as an antihalation underlayer, or as an antihalation overcoat. Additionally, one or more acutance dyes may be incorporated into one or more frontside layers such as the photothermographic emulsion layer, primer layer, underlayer, or topcoat layer (particularly on the frontside) according to known techniques. It is preferred that the photothermographic materials of this invention contain an antihalation coating on the support opposite to the side on which the emulsion and topcoat layers are coated.
Dyes useful as antihalation, filter, cross-over prevention (anti-crossover), anti-irradiation, and/or acutance dyes include squaraine dyes described in U.S. Pat. No. 5,380,635 (Gomez et al.), U.S. Pat. No. 6,063,560 (Suzuki et al.), U.S. Pat. No. 6,348,592 (Ramsden et al.), and EP 1 083 459 A1 (Kimura), the indolenine dyes described in EP-A 0342 810 (Leichter), and the cyanine dyes described in U.S. Ser. No. 10/011,892 (filed Dec. 5, 2001 by Hunt, Kong, Ramsden, and LaBelle). All of the above references are incorporated herein by reference.
Photothermographic materials having thermally developable layers disposed on both sides of the support often suffer from xe2x80x9ccrossover.xe2x80x9d Crossover results when radiation used to image one side of the photothermographic material is transmitted through the support and images the photothermographic layers on the opposite side of the support. Such radiation causes a lowering of image quality (especially sharpness). As crossover is reduced, the sharper becomes the image. Various methods are available for reducing crossover. Such xe2x80x9canti-crossoverxe2x80x9d materials can be materials specifically included for reducing crossover or they can be acutance or antihalation dyes. In either situation it is necessary that they be rendered colorless during processing.
Thus, it is also useful in the present invention to employ compositions including acutance, filter, anti-crossover, anti-irradiation, and/or antihalation dyes that will decolorize or bleach with heat during processing. Dyes and constructions employing these types of dyes are described in, for example, U.S. Pat. No. 5,135,842 (Kitchin et al.), U.S. Pat. No. 5,266,452 (Kitchin et al.), U.S. Pat. No. 5,314,795 (Helland et al.), U.S. Pat. No. 6,306,566, (Sakurada et al.), U.S. Published Application 2001-0001704 (Sakurada et al.), JP 2001-142175 (Hanyu et al.), and JP 2001-183770 (Hanye et al.). Also useful are bleaching compositions described in JP 11-302550 (Fujiwara), JP 2001-109101 (Adachi), JP 2001-51371 (Yabuki et al.), and JP 2000-029168 (Noro). All of the above references are incorporated herein by reference.
Particularly useful heat-bleachable, acutance, filter, anti-crossover, anti-irradiation, and/or antihalation compositions can include a radiation absorbing compound used in combination with a hexaarylbiimidazole (also known as a xe2x80x9cHABIxe2x80x9d), or mixtures thereof. Such HABI compounds are well known in the art, such as U.S. Pat. No. 4,196,002 (Levinson et al.), U.S. Pat. No. 5,652,091 (Perry et al.), and U.S. Pat. No. 5,672,562 (Perry et al.), all incorporated herein by reference. Additional examples of such heat-bleachable antihalation compositions include hexaarylbiimidazoles (HABI""s) used in combination with certain oxonol dyes as described for example in copending U.S. Ser. No. 09/875,772 (filed Jun. 6, 2001 by Goswami, Ramsden, Zielinski, Baird, Weinstein, Helber, and Lynch), or other dyes described for example in copending U.S. Ser. No. 09/944,573 (filed Aug. 31, 2001 by Ramsden and Baird), both incorporated herein by reference.
Under practical conditions of use, the compositions are heated to provide bleaching at a temperature of at least 90xc2x0 C. for at least 0.5 seconds. Preferably, bleaching is carried out at a temperature of from about 100xc2x0 C. to about 200xc2x0 C. for from about 5 to about 20 seconds. Most preferred bleaching is carried out within 20 seconds at a temperature of from about 110xc2x0 C. to about 130xc2x0 C.
The photothermographic materials of the present invention can be imaged in any suitable manner consistent with the type of material using any suitable imaging source (typically some type of radiation or electronic signal). The materials can be made sensitive to X-radiation or radiation in the ultraviolet region of the spectrum, the visible region of the spectrum, or the infrared region of the electromagnetic spectrum.
Imaging can be achieved by exposing the photothermographic materials of this invention to a suitable source of radiation to which they are sensitive, including X-radiation, ultraviolet light, visible light, near infrared radiation, and infrared radiation, to provide a latent image.
Suitable X-radiation imaging sources include general medical, mammographic, portal imaging, dental, industrial X-ray units, and other X-radiation generating equipment known to one skilled in the art. Also suitable are light-emitting screen-cassette systems of X-ray radiation units.
Other suitable exposure means are well known and include sources of radiation, including:incandescent or fluorescent lamps, xenon flash lamps, lasers, laser diodes, light emitting diodes, infrared lasers, infrared laser diodes, infrared light-emitting diodes, infrared lamps, or any other ultraviolet, visible, or infrared radiation source readily apparent to one skilled in the art, and others described in the art, such as in Research Disclosure, September, 1996, Item 38957. Particularly useful infrared exposure means include laser diodes, including laser diodes that are modulated to increase imaging efficiency using what is known as multi-longitudinal exposure techniques as described in U.S. Pat. No. 5,780,207 (Mohapatra et al.). Other exposure techniques are described in U.S. Pat. No. 5,493,327 (McCallum et al.).
Thermal development conditions will vary, depending on the construction used but will typically involve heating the imagewise exposed material at a suitably elevated temperature. Thus, the latent image can be developed by heating the exposed material at a moderately elevated temperature of, for example, from about 50xc2x0 C. to about 250xc2x0 C. (preferably from about 80xc2x0 C. to about 200xc2x0 C. and more preferably from about 100xc2x0 C. to about 200xc2x0 C.) for a sufficient period of time, generally from about 1 to about 120 seconds. Heating can be accomplished using any suitable heating means such as a hot plate, a steam iron, a hot roller or a heating bath.
In some methods, the development is carried out in two steps. Thermal development takes place at a higher temperature for a shorter time (for example at about 150xc2x0 C. for up to 10 seconds), followed by thermal diffusion at a lower temperature (for example at about 80xc2x0 C.) in the presence of a transfer solvent.
The photothermographic materials of the present invention are sufficiently transmissive in the range of from about 350 to about 450 nm in non-imaged areas to allow their use in a method where there is a subsequent exposure of an ultraviolet or short wavelength visible radiation sensitive imageable medium. For example, imaging the photothermographic material and subsequent development affords a visible image. The heat-developed photothermographic material absorbs ultraviolet or short wavelength visible radiation in the areas where there is a visible image and transmits ultraviolet or short wavelength visible radiation where there is no visible image. The heat-developed material may then be used as a mask and positioned between a source of imaging radiation (such as an ultraviolet or short wavelength visible radiation energy source) and an imageable material that is sensitive to such imaging radiation, such as a photopolymer, diazo material, photoresist, or photosensitive printing plate. Exposing the imageable material to the imaging radiation through the visible image in the exposed and heat-developed photothermographic material provides an image in the imageable material. This method is particularly useful where the imageable medium comprises a printing plate and the photothermographic material serves as an imagesetting film.
The present invention also provides a method for the formation of a visible image (usually a black-and-white image) by first exposing to electro-magnetic radiation and thereafter heating the inventive photothermographic material. In one embodiment, the present invention provides a method comprising:
A) imagewise exposing the photothermographic material of this invention to electromagnetic radiation to which the photosensitive silver halide of the material is sensitive, to form a latent image, and
B) simultaneously or sequentially, heating the exposed photothermographic material to develop the latent image into a visible image.
For example, the photothermographic material may be exposed in step A using any source of radiation to which they are sensitive, including ultraviolet light, visible light, near infrared radiation, infrared radiation, or any other radiation source readily apparent to one skilled in the art. One particularly preferred form of useful radiation is infrared radiation, including an infrared laser, an infrared laser diode, an infrared light-emitting diode, an infrared lamp, or any other infrared radiation source readily apparent to one skilled in the art.
This visible image can also be used as a mask for exposure of other photosensitive imageable materials, such as graphic arts films, proofing films, printing plates and circuit board films, that are sensitive to suitable imaging radiation (for example, UV radiation). This can be done by imaging an imageable material (such as a photopolymer, a diazo material, a photoresist, or a photosensitive printing plate) through the exposed and heat-developed photothermographic material. Thus, in some other embodiments wherein the photothermographic material comprises a transparent support, the image-forming method further comprises:
C) positioning the exposed and heat-developed photothermographic material with a visible image thereon, between a source of imaging radiation and an imageable material that is sensitive to the imaging radiation, and
D) thereafter exposing the imageable material to the imaging radiation through the visible image in the exposed and heat-developed photothermographic material to provide a visible image in the imageable material.
To further increase photospeed, the X-radiation sensitive photo-thermographic materials of this invention may be used in combination with one or more phosphor intensifying screens and/or metal screens in what is known as xe2x80x9cimaging assemblies.xe2x80x9d An intensifying screen absorbs X-radiation and emits longer wavelength electromagnetic radiation that the photosensitive silver halide more readily absorbs. Double-sided X-radiation sensitive photothermographic materials (that is, materials having one or more thermally developable imaging layers on both sides of the support) are preferably used in combination with two intensifying screens, one screen in the xe2x80x9cfrontxe2x80x9d and one screen in the xe2x80x9cbackxe2x80x9d of the material.
Such imaging assemblies are composed of a photothermographic material as defined herein (particularly one sensitive to X-radiation or visible light) and one or more phosphor intensifying screens adjacent the front and/or back of the material. These screens are typically designed to absorb X-rays and to emit electromagnetic radiation having a wavelength greater than 300 nm.
There are a wide variety of phosphors known in the art that can be formulated into phosphor intensifying screens, including but not limited to, the phosphors described in Research Disclosure, August 1979, Item 18431, Section IX, X-ray Screens/Phosphors, U.S. Pat. No. 2,303,942 (Wynd et al.), U.S. Pat. No. 3,778,615 (Luckey), U.S. Pat. No. 4,032,471 (Luckey), U.S. Pat. No. 4,225,653 (Brixner et al.), U.S. Pat. No. 3,418,246 (Royce), U.S. Pat. No. 3,428,247 (Yocon), U.S. Pat. No. 3,725,704 (Buchanan et al.), U.S. Pat. No. 2,725,704 (Swindells), U.S. Pat. No. 3,617,743 (Rabatin), U.S. Pat. No. 3,974,389 (Ferri et al.), U.S. Pat. No. 3,591,516 (Rabatin), U.S. Pat. No. 3,607,770 (Rabatin), U.S. Pat. No. 3,666,676 (Rabatin), U.S. Pat. No. 3,795,814 (Rabatin), U.S. Pat. No. 4,405,691 (Yale), U.S. Pat. No. 4,311,487 (Luckey et al.), U.S. Pat. No. 4,387,141 (Patten), U.S. Pat. No. 5,021,327 (Bunch et al.), U.S. Pat. No. 4,865,944 (Roberts et al.), U.S. Pat. No. 4,994,355 (Dickerson et al.), U.S. Pat. No. 4,997,750 (Dickerson et al.), U.S. Pat. No. 5,064,729 (Zegarski), U.S. Pat. No. 5,108,881 (Dickerson et al.), U.S. Pat. No. 5,250,366 (Nakajima et al.), U.S. Pat. No. 5,871,892 (Dickerson et al.), EP-A-0 491,116 (Benzo et al.), U.S. Pat. No. 4,988,880 (Bryan et al.), U.S. Pat. No. 4,988,881 (Bryan et al.), U.S. Pat. No. 4,994,205 (Bryan et al.), U.S. Pat. No. 5,095,218 (Bryan et al.), U.S. Pat. No. 5,112,700 (Lambert et al.), U.S. Pat. No. 5,124,072 (Dole et al.), U.S. Pat. No. 5,336,893 (Smith et al.), U.S. Pat. No. 4,835,397 (Arakawa et al.), U.S. Pat. No. 5,381,015 (Dooms), U.S. Pat. No. 5,464,568 (Bringley et al.), U.S. Pat. No. 4,226,653 (Brixner), U.S. Pat. No. 5,064,729 (Zegarski), U.S. Pat. No. 5,250,366 (Nakajima et al.), and U.S. Pat. No. 5,626,957 (Benso et al.), U.S. Pat. No. 4,368,390 (Takahashi et al.), and U.S. Pat. No. 5,227,253 (Takasu et al.), the disclosures of which are all incorporated herein by reference for their teaching of phosphors and formulation of phosphor intensifying screens.
Phosphor intensifying screens can take any convenient form providing they meet all of the usual requirements for use in radiographic imaging, as described for example in U.S. Pat. No. 5,021,327 (Bunch et al.), incorporated herein by reference. A variety of such screens are commercially available from several sources including by not limited to, LANEX(copyright), X-SIGHT(copyright) and InSight(copyright) Skeletal screens available from Eastman Kodak Company. The front and back screens can be appropriately chosen depending upon the type of emissions desired, the photicity desired, emulsion speeds, and % crossover. A metal (such as copper or lead) screen can also be included if desired.
Imaging assemblies can be prepared by arranging a suitable photothermographic material in association with one or more phosphor intensifying screens, and one or more metal screens in a suitable holder (often known as a cassette), and appropriately packaging them for transport and imaging uses.
Constructions and assemblies useful in industrial radiography include, for example, U.S. Pat. No. 4,480,024 (Lyons et al), U.S. Pat. No. 5,900,357 (Feumi-Jantou et al.), and EP 1 350 883 (Pesce et al.).